Electro-optical element including IMI coatings

ABSTRACT

An electrochromic element comprises a first substrate having a first surface and a second surface opposite the first surface, a second substrate in spaced-apart relationship to the first substrate and having a third surface facing the second surface and a fourth surface opposite the third surface, and an electrochromic medium located between the first and second substrates, wherein the electrochromic medium has a light transmittance that is variable upon application of an electric field thereto. The electrochromic element further comprises a transparent electrode layer covering at least a portion of at least a select one of the first surface, the second surface, the third surface, and the fourth surface, wherein the transparent electrode layer comprises an insulator/metal/insulator stack. The materials utilized to construct the insulator/metal/insulator stack are selected to optimize optical and physical properties of the electrochromic element such as reflectivity, color, electrical switch stability, and environmental durability.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/779,369, filed Mar. 3, 2006, entitled IMPROVED COATINGS AND REARVIEWELEMENTS INCORPORATING THE COATINGS, and U.S. Provisional ApplicationNo. 60/810,921, filed Jun. 5, 2006, entitled ELECTROCHROMIC REARVIEWMIRROR ASSEMBLY INCORPORATING A DISPLAY/SIGNAL LIGHT, both of which arehereby incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

This invention relates to electrochromic elements as utilized withinrearview mirror assemblies for motor vehicles, as well as within windowassemblies, and more particularly, to improved electrochromic elementsfor use within such assemblies. More particularly, the present inventionrelates to electrochromic elements that comprise transparent electrodelayers that include insulator/metal/insulator stacks.

Heretofore, various rearview mirrors for motor vehicles have beenproposed which change from the full reflectance mode (day) to thepartial reflectance mode(s) (night) for glare-protection purposes fromlight emanating from the headlights of vehicles approaching from therear. Similarly, variable transmittance light filters have been proposedfor use in architectural windows, skylights, within windows, sunroofs,and rearview mirrors for automobiles, as well as for windows or othervehicles such as aircraft windows. Among such devices are those whereinthe transmittance is varied by thermochromic, photochromic, orelectro-optic means (e.g., liquid crystal, dipolar suspension,electrophoretic, electrochromic, etc.) and where the variabletransmittance characteristic affects electromagnetic radiation that isat least partly in the visible spectrum (wavelengths from about 3800 Åto about 7800 Å). Devices of reversibly variable transmittance toelectromagnetic radiation have been proposed as the variabletransmittance element in variable transmittance light-filters, variablereflectance mirrors, and display devices, which employ suchlight-filters or mirrors in conveying information.

Devices of reversibly variable transmittance to electromagneticradiation, wherein the transmittance is altered by electrochromic means,are described, for example, by Chang, “Electrochromic andElectrochemichromic Materials and Phenomena,” in Non-emissiveElectrooptic Displays, A. Kmetz and K. von Willisen, eds. Plenum Press,New York, N.Y. 1976, pp. 155-196 (1976) and in various parts ofElectrochromism, P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, VCHPublishers, Inc., New York, N.Y. (1995). Numerous electrochromic devicesare known in the art. See, e.g., Manos, U.S. Pat. No. 3,451,741;Bredfeldt et al., U.S. Pat. No. 4,090,358; Clecak et al., U.S. Pat. No.4,139,276; Kissa et al., U.S. Pat. No. 3,453,038; Rogers, U.S. Pat. Nos.3,652,149, 3,774,988 and 3,873,185; and Jones et al., U.S. Pat. Nos.3,282,157, 3,282,158, 3,282,160 and 3,283,656. In addition to thesedevices, there are commercially available electrochromic devices andassociated circuitry, such as those disclosed in U.S. Pat. No.4,902,108, entitled “SINGLE-COMPARTMENT, SELF-ERASING, SOLUTION-PHASEELECTROCHROMIC DEVICES SOLUTIONS FOR USE THEREIN, AND USES THEREOF,”issued Feb. 20, 1990, to H. J. Byker; Canadian Patent No. 1,300,945,entitled “AUTOMATIC REARVIEW MIRROR SYSTEM FOR AUTOMOTIVE VEHICLES,”issued May 19, 1992, to J. H. Bechtel et al.; U.S. Pat. No. 5,128,799,entitled “VARIABLE REFLECTANCE MOTOR VEHICLE MIRROR,” issued Jul. 7,1992, to H. J. Byker; U.S. Pat. No. 5,202,787, entitled “ELECTRO-OPTICDEVICE,” issued Apr. 13, 1993, to H. J. Byker et al.; U.S. Pat. No.5,204,778, entitled “CONTROL SYSTEM FOR AUTOMATIC REARVIEW MIRRORS,”issued Apr. 20, 1993, to J. H. Bechtel; U.S. Pat. No. 5,278,693,entitled “TINTED SOLUTION-PHASE ELECTROCHROMIC MIRRORS,” issued Jan. 11,1994, to D. A. Theiste et al.; U.S. Pat. No. 5,280,380, entitled“UV-STABILIZED COMPOSITIONS AND METHODS,” issued Jan. 18, 1994, to H. J.Byker; U.S. Pat. No. 5,282,077, entitled “VARIABLE REFLECTANCE MIRROR,”issued Jan. 25, 1994, to H. J. Byker; U.S. Pat. No. 5,294,376, entitled“BIPYRIDINIUM SALT SOLUTIONS,” issued Mar. 15, 1994, to H. J. Byker;U.S. Pat. No. 5,336,448, entitled “ELECTROCHROMIC DEVICES WITHBIPYRIDINIUM SALT SOLUTIONS,” issued Aug. 9, 1994, to H. J. Byker; U.S.Pat. No. 5,434,407, entitled “AUTOMATIC REARVIEW MIRROR INCORPORATINGLIGHT PIPE,” issued Jan. 18, 1995, to F. T. Bauer et al.; U.S. Pat. No.5,448,397, entitled “OUTSIDE AUTOMATIC REARVIEW MIRROR FOR AUTOMOTIVEVEHICLES,” issued Sep. 5, 1995, to W. L. Tonar; and U.S. Pat. No.5,451,822, entitled “ELECTRONIC CONTROL SYSTEM,” issued Sep. 19, 1995,to J. H. Bechtel et al. Each of these patents is commonly assigned withthe present invention and the disclosures of each, including thereferences contained therein, are hereby incorporated herein in theirentirety by reference. Such electrochromic devices may be utilized in afully integrated inside/outside rearview mirror system or as separateinside or outside rearview mirror systems, and/or variable transmittancewindows.

FIG. 1 shows the cross-section of a typical electrochromic mirror device10, having a front planar substrate 12 and a rear planar substrate, andof which the general layout is known. A transparent conductive coating14 is provided on the rear face of the front element 12, and anothertransparent conductive coating 18 is provided on the front face of rearelement 16. A reflector 20, typically comprising a silver metal layer 20a covered by a protective copper metal layer 20 b, and one or morelayers of protective paint 20 c, is disposed on the rear face of therear element 16. For clarity of description of such a structure, thefront surface 12 a of the front glass element 12 is sometimes referredto as the first surface, and the inside surface 12 b of the front glasselement 12 is sometimes referred to as the second surface, the insidesurface 16 a of the rear glass element 16 is sometimes referred to asthe third surface, and the back surface 16 b of the rear glass element16 is sometimes referred to as the fourth surface. In the illustratedexample, the front glass element further includes an edge surface 12 c,while the rear glass element includes an edge surface 16 c. The frontand rear elements 12,16 are held in a parallel and spaced-apartrelationship by seal 22, thereby creating a chamber 26. Theelectrochromic medium 24 is contained in space or chamber 26. Theelectrochromic medium 24 is in direct contact with transparent electrodelayers 14 and 18, through which passes electromagnetic radiation whoseintensity is reversibly modulated in the device by a variable voltage orpotential applied to electrode layers 14 and 18 through clip contactsand an electronic circuit (not shown).

The electrochromic medium 24 placed in chamber 26 may includesurface-confined, electrode position-type or solution-phase-typeelectrochromic materials and combinations thereof. In an allsolution-phase medium, the electrochemical properties of the solvent,optional inert electrolyte, anodic materials, cathodic materials, andany other components that might be present in the solution arepreferably such that no significant electrochemical or other changesoccur at a potential difference which oxidizes anodic material andreduces the cathodic material other than the electrochemical oxidationof the anodic material, electrochemical reduction of the cathodicmaterial, and the self-erasing reaction between the oxidized form of theanodic material and the reduced form of the cathodic material.

In most cases, when there is no electrical potential difference betweentransparent conductors 14 and 18, the electrochromic medium 24 inchamber 26 is essentially colorless or nearly colorless, and incominglight (I_(O)) enters through the front element 12, passes through thetransparent coating 14, the electrochromic medium 24 in chamber 26, thetransparent coating 18, the rear element 16, and reflects off the layer20 a and travels back through the device and out the front element 12.Typically, the magnitude of the reflected image (I_(R)) with noelectrical potential difference is about 45 percent to about 85 percentof the incident light intensity (I_(O)). The exact value depends on manyvariables outlined below, such as, for example, the residual reflection(I′_(R)) from the front face of the front element, as well as secondaryreflections from the interfaces between the front element 12 and thefront transparent electrode 14, the front transparent electrode 14 andthe electrochromic medium 24, the electrochromic medium 24 and thesecond transparent electrode 18, and the second transparent electrode 18and the rear element 16. These reflections are well known in the art andare due to the difference in refractive indices between one material andanother as the light crosses the interface between the two. If the frontelement and the back element are not parallel, then the residualreflectance (I′_(R)) or other secondary reflections will not superimposewith the reflected image (I_(R)) from mirror surface 20 a, and a doubleimage will appear (where an observer would see what appears to be double(or triple) the number of objects actually present in the reflectedimage).

There are minimum requirements for the magnitude of the reflected imagedepending on whether the electrochromic mirrors are placed on the insideor the outside of the vehicle. For example, according to currentrequirements from most automobile manufacturers, inside mirrorspreferably have a high end reflectivity of at least 40 percent, andoutside mirrors must have a high end reflectivity of at least 35percent.

The electrode layers 14 and 18 are connected to electronic circuitrywhich is effective to electrically energize the electrochromic medium,such that when a potential is applied across the conductors 14 and 18,the electrochromic medium in chamber 26 darkens, such that incidentlight (I_(O)) is attenuated as the light passes toward the reflector 20a and as it passes back through after being reflected. By adjusting thepotential difference between the transparent electrodes, such a devicecan function as a “gray-scale” device, with continuously variabletransmittance over a wide range. For solution-phase electrochromicsystems, when the potential between the electrodes is removed orreturned to zero, the device spontaneously returns to the same,zero-potential, equilibrium color and transmittance as the device hadbefore the potential was applied. Other electrochromic materials areavailable for making electrochromic devices. For example, theelectrochromic medium may include electrochromic materials that aresolid metal oxides, redox active polymers, and hybrid combinations ofsolution-phase and solid metal oxides or redox active polymers; however,the above-described solution-phase design is typical of most of theelectrochromic devices presently in use.

Even before a fourth surface reflector electrochromic mirror such asthat shown in FIG. 1 was commercially available, various groupsresearching electrochromic devices had discussed moving the reflectorfrom the fourth surface to the third surface. Such a design hasadvantages in that it should, theoretically, be easier to manufacturebecause there are fewer layers to build into a device, i.e., the thirdsurface transparent electrode is not necessary when there is a thirdsurface reflector/electrode. Although this concept was described asearly as 1966, no group had commercial success because of the exactingcriteria demanded from a workable auto-dimming mirror incorporating athird surface reflector. U.S. Pat. No. 3,280,701, entitled “OPTICALLYVARIABLE ONE-WAY MIRROR,” issued Oct. 25, 1966, to J. F. Donnelly et al.has one of the earliest discussions of a third surface reflector for asystem using a pH-induced color change to attenuate light.

U.S. Pat. No. 5,066,112, entitled “PERIMETER COATED, ELECTRO-OPTICMIRROR,” issued Nov. 19, 1991, to N. R. Lynam et al., teaches anelectro-optic mirror with a conductive coating applied to the perimeterof the front and rear glass elements for concealing the seal. Although athird surface reflector is discussed therein, the materials listed asbeing useful as a third surface reflector suffer from the deficienciesof not having sufficient reflectivity for use as an inside mirror,and/or not being stable when in contact with a solution-phaseelectrochromic medium containing at least one solution-phaseelectrochromic material.

Others have broached the topic of a reflector/electrode disposed in themiddle of an all solid state-type device. For example, U.S. Pat. Nos.4,762,401, 4,973,141, and 5,069,535 to Baucke et al. teach anelectrochromic mirror having the following structure: a glass element, atransparent indium-tin-oxide electrode, a tungsten oxide electrochromiclayer, a solid ion conducting layer, a single layer hydrogenion-permeable reflector, a solid ion conducting layer, a hydrogen ionstorage layer, a catalytic layer, a rear metallic layer, and a backelement (representing the conventional third and fourth surface). Thereflector is not deposited on the third surface and is not directly incontact with electrochromic materials, certainly not at least onesolution-phase electrochromic material and associated medium.Consequently, it is desirable to provide an improved high reflectivityelectrochromic rearview mirror having a third surfacereflector/electrode in contact with a solution-phase electrochromicmedium containing at least one electrochromic material. Electrochromicwindows that have been proposed, typically include an electrochromiccell similar to that shown in FIG. 1, but without layer 20 a, 20 b and20 c.

While the adaptation of a reflective third surface electrochromic devicehas assisted in solving many problems, numerous deficiencies withinthese elements still exist. Various attempts have been made to providean electrochromic element with a second surface transparent conductiveoxide that is relatively low cost without sacrificing optical andphysical characteristics, such as reflectivity, color, electrical switchstability, and environmental durability. While previous approaches havefocused on indium tin oxide layers, these attempts have not effectivelysolved the myriad of problems noted above. Specifically, several issuessupport the development of transparent conductor alternatives toindium-tin oxide. For example, rapid switching electrochromic devicesrequire low sheet resistance materials on both sides of the associatedcell. Large electrochromic cells are particularly sensitive to sheetresistance, while high sheet resistance conductors lead to significantpotential drops across the conductor surfaces. These spatial potentialdrops reduce the local current density and slow the color change in theaffected area leading to effects such as irising. Other inherentdifficulties and failures associated with previous electrochromicsystems are set forth herein.

It is therefore desirable to provide an electrochromic element thatincludes a transparent electrode whose components reduce the overallcost of the electrochromic element without sacrificing optical andphysical characteristics, such as reflectivity, color, electrical switchstability, environmental durability and the like.

SUMMARY OF THE INVENTION

One aspect of the present invention is an electrochromic elementcomprising a first substrate having a first surface and a second surfaceopposite the first surface, a second substrate in spaced-apartrelationship to the first substrate and having a third surface facingthe second surface and a fourth surface opposite the third surface, andan electrochromic medium located between the first and secondsubstrates, wherein the electrochromic medium has a light transmittancethat is variable upon the application of an electric field thereto. Theelectrochromic element further comprises a transparent electrode layercovering at least a portion of at least a select one of the secondsurface and the third surface, wherein the transparent electrode layercomprises a first insulator layer, at least one metal layer, and asecond insulator layer, and wherein the electrochromic element displaysa color rendering index of greater than or equal to 80.

Another aspect of the present invention includes an electrochromicelement comprising a first substrate having a first surface and a secondsurface opposite the first surface, a second substrate in spaced-apartrelationship to the first substrate and having a third surface facingthe second surface and a fourth surface opposite the third surface, andan electrochromic medium located between the first and secondsubstrates, wherein the electrochromic medium has a light transmittancethat is variable upon the application of an electric field thereto. Theelectrochromic element further comprises a transparent electrode layercovering at least a portion of at least a select one of the secondsurface and the third surface, wherein the transparent electrode layercomprises a first insulator layer, at least one metal layer, and asecond insulator layer, and wherein at least a select one of the firstinsulator layer and the second insulator layer comprises at least aselect one of indium tin oxide, indium zinc oxide, aluminum zinc oxide,titanium oxide, CeOx, tin dioxide, silicon nitride, silicon dioxide,ZnS, chromium oxide, niobium oxide, ZrOx, WO3, nickel oxide, IRO2, andcombinations thereof.

Yet another aspect of the present invention is an electrochromic elementthat comprises a first substrate having a first surface and a secondsurface opposite the first surface, a second substrate in spaced-apartrelationship to the first substrate and having a third surface facingthe second surface and a fourth surface opposite the third surface, andan electrochromic medium located between the first and secondsubstrates, wherein the electrochromic medium has a light transmittancethat is variable upon the application of an electric field thereto. Theelectrochromic element further comprises a transparent electrode layercovering at least a portion of at least a select one of the secondsurface and the third surface, wherein the transparent electrode layercomprises a first insulator layer, a metal layer, and a second insulatorlayer, and wherein at least one of the first insulator layer and thesecond insulator layer and at least one barrier layer between aninsulator layer and the metal layer wherein the barrier layer comprisesat least a select one gold, ruthenium, rodium, palladium, cadmium,copper, nickel, platinum, iridium, and combinations thereof.

Still yet another aspect of the present invention is an electrochromicelement that comprises a first substrate having a first surface and asecond surface opposite the first surface, a second substrate inspaced-apart relationship to the first substrate and having a thirdsurface facing the second surface and a fourth surface opposite thethird surface, and an electrochromic medium located between the firstand second substrates, wherein the electrochromic medium has a lighttransmittance that is variable upon the application of an electric fieldthereto. The electrochromic element further comprises a transparentelectrode layer covering at least a portion of at least a select one ofthe second surface and the third surface, wherein the transparentelectrode layer comprises a first insulator layer, a metal layer, and asecond insulator layer, and wherein the metal layer comprises silver andat least one of the first insulator layer and the second insulator layercomprises indium tin oxide, indium zinc oxide, aluminum zinc oxide,titanium oxide, CeOx, tin dioxide, silicon nitride, silicon dioxide,ZnS, chromium oxide, niobium oxide, ZrOx, WO3, nickel oxide, IRO2, andcombinations thereof.

Still yet another aspect of the present invention is a method formanufacturing an electrochromic element, wherein the method comprisesproviding a first substrate having a first surface and a second surfaceopposite the first surface, providing a second substrate having a thirdsurface facing the second surface and a fourth surface opposite thethird surface, and applying a transparent electrode layer to at least asecond one of the second surface and the third surface, wherein thetransparent electrode layer comprises a first insulator layer, a metallayer, and second insulator layer. The method further includes applyingan epoxy to at least a select one of the second surface and the thirdsurface, and sealing the first substrate to the second substrate byapplying an infrared radiation to the epoxy, wherein the minimumwavelength of the infrared radiation is 2.5 μm.

The present inventive electrochromic element includes a transparentelectrode whose components reduce the overall cost of the electrochromicelement without sacrificing optical and physical characteristics, suchas reflectivity, color, electrical switch stability, environmentaldurability and the like. Moreover, the inventive electrochromic elementis relatively easy to manufacture, assists in providing a robustmanufacturing process, provides versatility in selection of componentsutilized in constructing insulator/metal/insulator stacks, and allowstailored construction thereof to achieve particular optical and physicalproperties.

These and other features, advantages, and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims, andappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an enlarged cross-sectional view of a prior art electrochromicmirror assembly incorporating a fourth surface reflector;

FIG. 2 is a front elevational view schematically illustrating aninside/outside electrochromatic rearview mirror system for motorvehicles;

FIG. 3 is an enlarged cross-sectional view of an electrochromic mirrorincorporating a third surface reflector/electrode taken along the lineIII-III, FIG. 2;

FIG. 4 is a further enlarged cross-sectional view of a transparentelectrode of the area IV, FIG. 3;

FIG. 5 is a graph of reflectance/transmittance versus wavelength of ITOon glass within an incident medium of air or electrochromic fluid;

FIG. 6A-6C are graphs of difference in transmittance between and IMIwith air and EC fluid as the incident media for different combinationsof layer thickness in a 3-layer IMI stack;

FIG. 7 is a graph of change to transmittance versus soak time of a fivelayer IMI stack;

FIG. 8 is a graph of a change to resistance versus soak time of a fivelayer IMI stack;

FIG. 9 is a graph of sheet resistance and transmittance versus oxygenpercentage of a two-layer IMI stack;

FIG. 10 is a graph of oxygen percentage versus extinction coefficientversus percent roughness of the two-layer IMI stack; and

FIG. 11 is a graph of wavelength versus reflectance for DOE2 sample 7,8, and 13.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For purposes of description herein, the terms “upper,” “lower,” “right,”“left,” “rear,” “front,” “vertical,” “horizontal,” and derivativesthereof shall relate to the invention as oriented in FIGS. 1 and 3.However, it is to be understood that the invention may assume variousalternative orientations and step sequences, except where expresslyspecified to the contrary. It is also to be understood that the specificdevices and processes illustrated in the attached drawings, anddescribed in the following specification are exemplary embodiments ofthe inventive concepts defined in the appended claims. Hence, specificdimensions and other physical characteristics relating to theembodiments disclosed herein are not to be considered as limiting,unless the claims expressly state otherwise.

FIG. 2 shows a front elevational view schematically illustrating avehicle mirror system 100 that includes an inside mirror assembly 110and two outside rearview mirror assemblies 111 a and 111 b for thedriver-side and passenger-side, respectively, all of which are adaptedto be installed on a motor vehicle in a conventional manner and wherethe mirrors face the rear of the vehicle and can be viewed by the driverof the vehicle to provide a rearward view. While mirror assemblies ingeneral are utilized herein to describe the present invention, it isnoted that this invention is equally applicable to the construction ofelectrochromic windows. The inside mirror assembly 110 and the outsiderearview mirror assemblies 111 a, 111 b may incorporate light-sensingelectronic circuitry of the type illustrated and described in theabove-referenced Canadian Patent No. 1,300,945, U.S. Pat. No. 5,204,778,or U.S. Pat. No. 5,451,822, and other circuits capable of sensing glareand ambient light and supplying a drive voltage to the electrochromicelement. In the illustrated example, electrical circuitry 150 isconnected to and allows control of the potential to be applied acrossthe reflector/electrode 120 and transparent electrode 128, such thatelectrochromic medium 126 will darken and thereby attenuate variousamounts of light traveling therethrough and then vary the reflectance ofthe mirror containing the electrochromic medium 126. The mirrorassemblies 110, 111 a, 111 b are similar in that like numbers identifycomponents of the inside and outside mirrors. These components may beslightly different in configuration, but function in substantially thesame manner and obtain substantially the same results as similarlynumbered components. For example, the shape of the front glass elementof the inside mirror 110 is generally longer and narrower than theoutside mirrors 111 a, 111 b. There are also some different performancestandards placed on the inside mirror 110 compared with the outsidemirrors 111 a, 111 b. For example, the inside mirror 110 generally, whenfully cleared, should have a reflectance value of about 50 percent toabout 85 percent or higher, whereas the outside mirrors often have areflectance of about 50 percent to about 65 percent. Also, in the UnitedStates (as supplied by the automobile manufacturers), the passenger-sidemirror 111 b typically has a spherically bent or convex shape, whereasthe driver-side mirror 111 a and the inside mirror 110 presently must beflat. In Europe, the driver-side mirror 111 a is commonly flat oraspheric, whereas the passenger-side mirror 111 b has a convex shape. InJapan, both of the outside mirrors 111 a, 111 b have a convex shape. Thefollowing description is generally applicable to all mirror assembliesof the present invention, while the general concepts are equallyapplicable to the construction of electrochromic windows.

FIG. 3 shows a cross-sectional view of the mirror assembly 111 a havinga front transparent substrate 112 having a front surface 112 a and arear surface 112 b, and a rear susbtrate 114 having a front surface 114a and a rear surface 114 b. For clarity of description of such astructure, the following designations will be used hereinafter. Thefront surface 112 a of the front substrate will be referred to as thefirst surface 112 a, and the back surface 112 b of the front substrateas the second surface 112 b. The front surface 114 a of the rearsubstrate will be referred to as the third surface 114 a, and the backsurface 114 b of the rear substrate as the fourth surface 114 b. Thefront substrate 112 further includes an edge surface 112 c, while therear substrate 114 further includes an edge surface 114 c. A chamber 125is defined by a layer of transparent conductor 128 (carried on thesecond surface 112 b), a reflector/electrode 120 (disposed on the thirdsurface 114 a), and an inner circumferential wall 132 of a sealingmember 116. An electrochromic medium 126 is contained within the chamber125.

As broadly used and described herein, the reference to an electrode orlayer as being “carried” on or applied to a surface of an element,refers to both electrodes or layers that are disposed directly on thesurface of an element or disposed on another coating, layer or layersthat are disposed directly on the surface of the element. Further, it isnoted that the mirror assembly 111 a is described for illustrativepurposes only, and that the specific components and elements may berearranged therein, such as the configuration illustrated in FIG. 1, andthose configurations known for electrochromic windows.

The front transparent substrate 112 may be any material which istransparent and has sufficient strength to be able to operate in theconditions, e.g., varying temperatures and pressures, commonly found inthe automotive environment. The front substrate 112 may comprise anytype of borosilicate glass, soda lime glass, float glass, or any othermaterial, such as, for example, a polymer or plastic, that istransparent in the visible region of the electromagnetic spectrum. Thefront substrate 112 is preferably a sheet of glass. The rear substrate114 must meet the operational conditions outlined above, except that itdoes not need to be transparent in all applications, and therefore maycomprise polymers, metals, glass, ceramics, and preferably is a sheet ofglass.

The coatings of the third surface 114 a are sealably bonded to thecoatings on the second surface 112 b in a spaced-apart and parallelrelationship by the seal member 116 disposed near the outer perimeter ofboth the second surface 112 b and the third surface 114 a. The sealmember 116 may be any material that is capable of adhesively bonding thecoatings on the second surface 112 b to the coatings on the thirdsurface 114 a to seal the perimeter such that the electrochromicmaterial 126 does not leak from within the chamber 125. Optionally, thelayer of transparent conductive coating 128 and the layer ofreflector/electrode 120 may be removed over a portion where the sealmember 116 is disposed (not the entire portion, otherwise the drivepotential could not be applied to the two coatings). In such a case, theseal member 116 must bond well to glass.

The performance requirements for the perimeter seal member 116 used inan electrochromic device are similar to those for a perimeter seal usedin a liquid crystal device (LCD), which are well known in the art. Theseal 116 must have good adhesion to glass, metals and metal oxides; musthave low permeabilities for oxygen, moisture vapor, and otherdetrimental vapors and indium; and must not interact with or poison theelectrochromic or liquid crystal material it is meant to contain andprotect. The perimeter seal 116 can be applied by means commonly used inthe LCD industry, such as by silk-screening or dispensing. Totallyhermetic seals, such as those made with glass frit or solder glass, canbe used, but the high temperatures involved in processing (usually near450° C.) this type of seal can cause numerous problems, such as glasssubstrate warpage, changes in the properties of transparent conductiveelectrode, and oxidation or degradation of the reflector. Because oftheir lower processing temperatures, thermoplastic, thermosetting or UVcuring organic sealing resins are preferred. Such organic resin sealingsystems for LCDs are described in U.S. Pat. Nos. 4,297,401, 4,418,102,4,695,490, 5,596,023, and 5,596,024. Because of their excellent adhesionto glass, low oxygen permeability and good solvent resistance,epoxy-based organic sealing resins are preferred. These epoxy resinseals may be UV curing, such as described in U.S. Pat. No. 4,297,401, orthermally curing, such as with mixtures of liquid epoxy resin withliquid polyamide resin or dicyandiamide, or they can be homopolymerizedThe epoxy resin may contain fillers or thickeners to reduce flow andshrinkage such as fumed silica, silica, mica, clay, calcium carbonate,alumina, etc., and/or pigments to add color. Fillers pretreated withhydrophobic or silane surface treatments are preferred. Cured resincrosslink density can be controlled by use of mixtures ofmono-functional, di-functional, and multi-functional epoxy resins andcuring agents. Additives such as silanes or titanates can be used toimprove the seal's hydrolytic stability, and spacers such as glass beadsor rods can be used to control final seal thickness and substratespacing. Suitable epoxy resins for use in a perimeter seal member 116include, but are not limited to: “EPON RESIN” 813, 825, 826, 828, 830,834, 862, 1001F, 1002F, 2012, DPS-155, 164, 1031, 1074, 58005, 58006,58034, 58901, 871, 872, and DPL-862 available from Shell Chemical Co.,Houston, Tex.; “ARALITE” GY 6010, GY 6020, CY 9579, GT 7071, XU 248, EPN1139, EPN 1138, PY 307, ECN 1235, ECN 1273, ECN 1280, MT 0163, MY 720,MY 0500, MY 0510, and PT 810 available from Ciba Geigy, Hawthorne, N.Y.;and “D.E.R.” 331, 317, 361, 383, 661, 662, 667, 732, 736, “D.E.N.” 431,438, 439 and 444 available from Dow Chemical Co., Midland, Mich.Suitable epoxy curing agents include V-15, V-25, and V-40 polyamidesfrom Shell Chemical Co.; “AJICURE” PN-23, PN-34, and VDH available fromAjinomoto Co., Tokyo, Japan; “CUREZOL” AMZ, 2MZ, 2E4MZ, C11Z, C17Z, 2PZ,2IZ, and 2P4MZ available from Shikoku Fine Chemicals, Tokyo, Japan;“ERISYS” DDA or DDA accelerated with U-405, 24EMI, U-410, and U-415available from CVC Specialty Chemicals, Maple Shade, N.J.; and “AMICURE”PACM, 352, CG, CG-325, and CG-1200 available from Air Products,Allentown, Pa. Suitable fillers include fumed silica such as “CAB-O-SIL”L-90, LM-130, LM-5, PTG, M-5, MS-7, MS-55, TS-720, HS-5, and EH-5available from Cabot Corporation, Tuscola, Ill.; “AEROSIL” R972, R974,R805, R812, R812S, R202, US204, and US206 available from Degussa, Akron,Ohio. Suitable clay fillers include BUCA, CATALPO, ASP NC, SATINTONE 5,SATINTONE SP-33, TRANSLINK 37, TRANSLINK 77, TRANSLINK 445, andTRANSLINK 555 available from Engelhard Corporation, Edison, N.J.Suitable silica fillers are SILCRON G-130, G-300, G-100-T, and G-100available from SCM Chemicals, Baltimore, Md. Suitable silane couplingagents to improve the seal's hydrolytic stability are Z6020, Z-6030,Z-6032, Z-6040, Z-6075, and Z-6076 available from Dow ComingCorporation, Midland, Mich. Suitable precision glass microbead spacersare available in an assortment of sizes from Duke Scientific, Palo Alto,Calif.

The electrochromic medium 126 is capable of attenuating light travelingtherethrough and has at least one solution-phase electrochromic materialin intimate contact with the reflector/electrode 120 and at least oneadditional electro-active material that may be solution-phased,surface-confined, while one that plates out onto a surface. However, thepresently preferred medium are solution-phased redox electrochromics,such as those disclosed in U.S. Pat. Nos. 4,902,108; 5,128,799;5,278,693; 5,280,380; 5,282,077; 5,294,376; and 5,336,448. U.S. Pat. No.6,020,987 entitled “AN IMPROVED ELECTRO-CHROMIC MEDIUM CAPABLE OFPRODUCING A PRE-SELECTED COLOR, DISCLOSES ELECTRO-CHROMIC MEDIUM THATARE PERCEIVED TO BE GREY THROUGH THEIR NORMAL RANGE OF OPERATION.” Theentire disclosure of this patent is hereby incorporated by referenceherein. If a solution-phase electrochromic medium is utilized, it may beinserted into chamber 125 through a sealable fill port 142 throughwell-known techniques.

It is known in the electrochromic art that a mirror or window may notdarken uniformly when an electrical potential is applied to the element.The non-uniform darkening results from local differences in electricalpotential across the solid state electrochromic materials, fluid or gelin an electrochromic element. The electrical potential across theelement varies with the sheet resistance of the electrodes, the bus barconfiguration, the conductivity of the electrochromic medium, theconcentration of the electrochromic medium, the cell spacing or distancebetween the electrodes, and the distances from the bus bars. A commonlyproposed solution to this problem is to make the coatings or layerscomposing the electrodes thicker thus reducing their sheet resistanceand enabling a faster darkening element. As will be discussed belowthere are practical penalties that are imparted that restrict thissimplistic approach to solving the problem. In many instances thepenalties make an electrochromic element unsuitable for a givenapplication. In at least one embodiment of the present inventionimproved electrode materials, methods of manufacturing said electrodesand bus bar configurations are described that solve problems that arisewith simply thickening the electrode layers and result in electrochromicelements with faster, more uniform darkening characteristics.

In a typical inside mirror the bus bars run parallel to the longdimension. This is to minimize the potential drop across the partbetween the electrodes. The mirror also typically consists of a highsheet resistance transparent electrode and a lower sheet resistancereflector electrode. The mirror will darken most quickly near the busbar for the higher sheet resistance electrode and slowest at someintermediate position between the two electrodes. Near the bus bar forthe lower sheet resistance electrode will have a darkening rate betweenthese two values. There is a variation in effective electrical potentialas one moves between the two bus bars. In the case of two long parallelbus bars that have a relatively short distance between them (distancebetween the bus bars is less than half the length of the bus bars) themirror will darken in a “window shade” fashion. This means that themirror darkens faster near one bus and the darkening appears to movebetween the two bus bars in a gradual fashion. Typically, the darkeningrate is measured at the middle of the part and in the case of a mirrorwith a width to height ratio greater than 2, any non-uniformities indarkening rate are relatively minor.

As the size of the mirrors increases, and along with it the distancebetween the bus bars, the relative difference in the darkening rateacross the parts also increases. This can be exacerbated when themirrors are designed for an outside application. The metals that canwithstand the rigors of such an environment typically have lowerconductivity than metals such as silver or silver alloys that aresuitable and common for inside mirror applications. A metal electrodefor an outside application may therefore have a sheet resistance up to 6ohms/sq while an inside mirror may have a sheet resistance of <0.5ohms/sq. In other outside mirror applications the transparent electrodemay be limited in thickness for various optical requirements. Thetransparent electrode, such as ITO, is often limited to a ½ wavethickness in the most common usage as described in U.S. PatentApplication No. 60/888,686, entitled ELECTRO-OPTICAL ELEMENT WITHIMPROVED TRANSPARENT CONDUCTOR, which is incorporated herein byreference. This limitation is due to properties of the ITO discussedherein but also due to the expense associated with making an ITO coatingthicker. In other applications the coating is limited to 80% of the ½wave thickness. Both of these thickness constraints limit the sheetresistance of the transparent electrode to greater than about 12 ohm/sqfor a ½ wave and up to 17-18 ohms/sq for a coating that is 80% of a ½wave coating. The higher sheet resistance of the metal and transparentelectrodes results in a slower, less uniform darkening mirror.

The darkening rate may be estimated from an analysis of theelectrochromic element in terms of an electrical circuit. The discussionbelow pertains to coatings that have uniform sheet resistance across theelement. The potential at any location between parallel electrodes issimply a function of the sheet resistance of each electrode and theresistance of the electrochromic medium. In Table 1 below, the averagepotential across the element between the electrodes is presented alongwith the difference between the maximum and minimum potential. Thisexample is for an element with a 10 cm spacing between the parallel busbars, a 180 micron cell spacing, a 1.2 volt driving voltage and 100,000Ohm*cm fluid resistivity. Six combinations of top and bottom electrodesheet resistance are compared.

TABLE 1 Ex: 1 Ex: 2 Ex: 3 Ex: 4 Ex: 5 Ex: 6 Top Plate Sheet Resistance(ohm/sq) 17 17 12 12 9 9 Bottom Plate Sheet Resistance (ohm/sq) 5 0.5 50.5 5 0.5 Distance Between Electrodes (cm) 10 10 10 10 10 10 CellSpacing (um) 180 180 180 180 180 180 Fluid Resistivity (Ohm * cm) 100000100000 100000 100000 100000 100000 Driving Potential (V) 1.2 1.2 1.2 1.21.2 1.2 Finite Element Width (cm) 1 1 1 1 1 1 Potential at Anode (V)1.168 1.197 1.168 1.197 1.168 1.197 Potential at Cathode (V) 1.096 1.0961.125 1.125 1.143 1.143 Average Potential (V) 1.131 1.145 1.146 1.1601.155 1.169

The speed of darkening is fastest at the electrical contact to thehighest sheet resistance electrode and is related to the effectivepotential at this position. The higher the effective potential adjacentto this electrical contact (or elsewhere) the faster the averagedarkening of the mirror will be. The fastest overall darkening time willoccur when the potential is as high as possible across the part. Thiswill drive the electrochemistry to darken at an accelerated rate. Thesheet resistance of the coatings on both the top and bottom substratesplays a role in determining the effective potential between theelectrodes, but as can be seen from the table the high sheet resistanceelectrode plays a more critical role. In past electrochromic art theimprovements were driven almost exclusively by lowering the sheetresistance of the low resistance electrode, due to the use of materialssuch as silver that provided substantive benefits and was relativelyeasy to implement.

The overall rate can be increased as the driving potential is increasedbut the trends will be constant independent of the driving voltage.Further, the current draw at a given voltage influences the darkeninguniformity. Uniformity can be improved by adjustments to cell spacing,concentration, or choice of electrochromic materials, but oftenimprovements in uniformity using these adjustments can have a negativeimpact on darkening speed, clearing speed or both darkening and clearingspeed. For example, increasing cell spacing and decreasing fluidconcentration will decrease the current draw and will thereby improveuniformity, but the clearing time will increase. Therefore, the sheetresistance of the layers must be appropriately set to attain both speedof darkening and uniformity of darkening. Preferably the sheetresistance of the transparent electrode should be less than 11.5ohms/sq, preferably less than 10.5 ohms/sq and more preferably less than9.5 ohms/sq and due to the optical requirements discussed below, in someembodiments, the thickness of the transparent electrode should be lessthan about a half wave optical thickness. Alternatively, the transparentelectrode may comprise an IMI type coating. The reflector electrodeshould be less than about 3 ohms/sq, preferably less than about 2ohms/sq and most preferably less than 1 ohm/sq. A mirror orelectrochromic element so constructed will also have a relativelyuniform darkening such that the difference in darkening time between thefastest and slowest darkening rate is less than a factor of 3,preferably less than a factor of 2 and most preferably less than afactor of 1.5. Novel, high-performance, low-cost materials are discussedbelow that enable these fast, uniform darkening elements.

In other applications it may be impractical to have two relativelyparallel bus bars. This may be due to an uneven shape common withoutside mirrors. In other circumstance it may be desirable to have apoint contact to the low resistance electrode. The point contact mayenable the minimization or elimination of the laser deletion line usedin some applications. The use of a point contact simplifies or ispreferential for some aspects of the mirror construction but it makes itdifficult to achieve a relative uniform potential across the part. Theelimination of the relatively long bus along the low resistancereflector electrode effectively increases the resistance of theelectrode. Therefore, novel combinations of bus bars and coating sheetresistance values are needed to attain fast, uniform darkening.

As noted above one skilled in the art would have anticipated that itwould require extremely low sheet resistance values on the metalreflector electrode to enable a point contact scheme. However, it isnecessary to have a lower sheet resistance for the transparent electrodeto improve the uniformity. Table 2 shows the results of the uniformityexperiments. In this test we made solution phase electrochromic elementsthat were approximately 8 inches wide by 6 inches tall. The benefits ofelement designs discussed herein pertain predominantly to largeelements. A large element is defined as one that has the minimumdistance from the edge of any point on the edge of the viewing area tothe geometric center is greater than approximately 5 cm. Lack of uniformdarkening becomes even more problematic when the distance is greaterthan approximately 7.5 cm and even more problematic when the distance isgreater than approximately 10 cm. The sheet resistance of thetransparent electrode (ITO) and the metal reflector were varied as notedin Table 2. Contact was made to the metal electrode with a pointcontact. A clip contact such as the so called J-clip was used with an Agpaste line approximately 1″ long to provide electrical contact to themetal reflector along one of the short length sides of the mirror.Electrical contact was made to the transparent electrode via an Ag pastealong the one side opposite the point contact and continuing down onethird of the distance along both long sides of the mirror. The darkeningtime (T5515) was measured at three locations on the mirror. Position 1is near the point contact, position 2 is at the edge of the transparentelectrode bus opposite the point contact and position 3 is at the centerof the mirror. The T5515 time (in seconds) is the time it takes themirror to go from 55% reflectance to 15% reflectance. The maxreflectance is the maximum reflectance of the mirror. The delta T5515 isthe time difference between either point 1 and point 2 or between point2 and point 3. This is a measure of the difference in darkening ratebetween the fastest position and the other two locations on the mirror.As the darkening becomes more uniform these numbers become closertogether. The timing factor is the darkening time at a given positiondivided by the time at the fastest position. This shows the relativescaling of time between the different locations independent of theabsolute rate at any given location. As noted above, it is preferred tohave a timing factor less than 3 and preferable less than 2 and mostpreferably less than 1.5. It can be seen from Table 2 that we do notattain a timing factor of 3 when the ITO sheet resistance is at 14ohms/sq for this particular mirror configuration. All three exampleswith an ITO with 9 ohms per square have timing factors less than 3. Thecenter of mirror reading is the location that deviates most from thefastest location. A statistical analysis was conducted on this datawhich revealed unexpectedly that the ITO sheet resistance was the solefactor that contributed to the timing factor. Using the statisticalmodels an ITO sheet resistance of less than about 11.5 ohms/sq is neededto have a timing factor of 3.0 or less for this embodiment. Using thesame statistical models the ITO must have a sheet resistance of lessthan 7 ohms/sq for the timing factor to be less than 2.0 for this mirrorconfiguration. Even though the timing factor is not affected by thesheet resistance of the third surface reflector the overall darkeningrate is affected. When the sheet resistance of said reflector is lessthan or equal to 2 ohms/sq and the ITO is at approximately 9 ohms/sq thedarkening rate for this mirror is less than 8 seconds in the center.This value corresponds approximately to a mirror of similar size with aconventional bus arrangement. Therefore, by lowering the sheetresistance of the ITO a point contact is enabled with a relatively highsheet resistance reflector.

TABLE 2 Meas- Reflector ITO urement Max delta timing ohms/sq ohm/sqPosition Reflectance T5515 T5515 factor 0.5 9 1 55.3 3.7 1.3 1.6 0.5 9 255.5 2.3 0.5 9 3 55.3 6.0 3.7 2.6 1 9 1 56.0 5.4 2.3 1.7 1 9 2 56.0 3.11 9 3 56.0 7.2 4.1 2.3 2 9 1 55.8 5.0 1.9 1.6 2 9 2 55.9 3.1 2 9 3 55.97.8 4.6 2.5 0.5 14 1 56.5 5.6 2.8 2.0 0.5 14 2 56.6 2.9 0.5 14 3 56.510.2 7.3 3.6 1 14 1 57.6 6.8 3.4 2.0 1 14 2 57.6 3.4 1 14 3 57.5 12.28.8 3.6 2 14 1 57.3 8.4 4.4 2.1 2 14 2 57.5 4.0 2 14 3 57.4 14.0 9.9 3.5

The unexpected role of the sheet resistance of the ITO in the uniformityand speed of darkening was expanded on in another set of experiments. Inthese experiments the length of bus bar contact to the higher sheetresistance electrode, in this example ITO, was extended further down thesides of the mirror and even onto the bottom edge of the mirror in somecases. Table 3 demonstrates the effect on uniformity with changes in buslength. In these tests the element shape and configuration are the sameas for Table B above except where noted. The contact percentage is apercentage comparison of the bus bar length of the ITO contact comparedto the total length of the perimeter. The bus bar ratio is the length ofthe ITO contact relative to the small reflector contact of approximately2 cm or less.

The data from Table 3 show that increasing the bus length of the highersheet resistance electrode significantly improves uniformity. For the 2ohm/sq. reflector, increasing the length of the bus contact from 40% to85% improves the timing factor from 2.4 to 1.7. For the 0.5 ohm/sqreflector, the same change in ITO bus length from 40 to 85% improves thetiming factor from 3.2 to 1.2 and significantly improves the darkeningrate. It is noted that the element with the lower sheet resistancereflector is generally faster to darken than the comparable 2 ohm/sq.case, but the uniformity of the 0.5 ohm case with a shorter ITO contactis actually worse as demonstrated by the timing factor. The increase buslength to the ITO is particularly helpful for the element with the 0.5ohm/sq. reflector.

When the contact percentage is increased, the position of the fastestand slowest darkening can change as well. In this example higher contactpercentage significantly improves the darkening times at both positions1 and 3 and the corresponding timing factors.

TABLE 3 Contact Bus Bar Reflector ITO Measurement Max delta timingPercentage Ratio ohms/sq ohm/sq Position Reflectance T5515 T5515 factor85 20 2 9 1 57.0 2.9 85 20 2 9 2 57.0 3.7 0.8 1.3 85 20 2 9 3 57.3 4.81.9 1.7 58 13 2 9 1 56.6 3.4 58 13 2 9 2 57.2 3.5 2.2 1.0 58 13 2 9 357.5 5.6 2.2 1.6 40 9 2 9 1 56.9 8 4.6 2.4 40 9 2 9 2 57.3 3.4 40 9 2 93 57.4 8.2 4.8 2.4 85 20 0.5 9 1 56.0 3 85 20 0.5 9 2 56.2 3 85 20 0.5 93 56.1 3.5 0.5 1.2 58 13 0.5 9 1 55.8 4 1.5 1.6 58 13 0.5 9 2 56.1 2.558 13 0.5 9 3 56.0 3.5 1 1.4 40 9 0.5 9 1 55.5 8.2 5.6 3.2 40 9 0.5 9 255.8 2.6 40 9 0.5 9 3 56.0 4.9 2.3 1.9

These experiments demonstrate that when using a short bus with the lowsheet resistance electrode it is beneficial to increase the bus lengthto the opposite electrode to improve uniformity. Ideally, therefore forlarge mirrors we prefer the ratio of the lengths of the bus bars to begreater than 5:1, preferably greater than 9:1, even more preferablygreater than 13:1 and most preferably greater than 20:1 to attain atiming factor below 3. We also find that independent of the length ofthe smaller bus that uniformity improves by increasing the length of thebus to the higher sheet resistance electrode to acquire a contactpercentage preferably greater than approximately 58% and more preferablygreater than approximately 85%. Typical large EC mirrors have a contactpercentage less than 50%. The examples noted above use ITO as thetransparent electrode. Alternatively, an IMI coating as described hereinmay be used with comparable speed and uniformity results.

A combination reflector/electrode 120 is disposed on the third surface114 a and comprises at least one layer of a reflective material 121which serves as a mirror reflectance layer and also forms an integralelectrode in contact with and in a chemically and electrochemicallystable relationship with any constituents in an electrochromic medium.As stated above, the conventional method of building electrochromicdevices was to incorporate a transparent conductive material on thethird surface as an electrode, and place a reflector on the fourthsurface. By combining the “reflector” and “electrode” and placing bothon the third surface, several advantages arise which not only make thedevice manufacture less complex, but also allow the device to operatewith higher performance. For example, the combined reflector/electrode120 on the third surface 114 a generally has higher conductivity than aconventional transparent electrode and previously usedreflector/electrodes, which allows greater design flexibility. One caneither change the composition of the transparent conductive electrode128 on the second surface 112 b to one that has lower conductivity(being cheaper and easier to produce and manufacture) while maintainingcoloration speeds similar to that obtainable with a fourth surfacereflector device, while at the same time decreasing substantially theoverall cost and time to produce the electrochromic device. If, however,performance of a particular design is of utmost importance, a moderateto high conductivity transparent electrode can be used on the secondsurface, such as, for example, ITO, IMI, etc. The combination of thehigh conductivity (corresponding to sheet resistance of less than, e.g.,250 Ohms/square, preferably less than 15Ohms/square) reflector/electrode120 on the third surface 114 a and the high conductivity transparentelectrode 128 on the second surface 112 b will not only produce anelectrochromic device with more even overall coloration, but will alsoallow for increased speed of coloration and clearing. Furthermore,fourth surface reflector mirror assemblies include two transparentelectrodes with relatively low conductivity, and in previously usedthird surface reflector mirrors there is a transparent electrode and areflector/electrode with relatively low conductivity and, as such, along bus bar on the front and rear element to bring current in and outis necessary to ensure adequate coloring speed.

The layer of a transparent electrically conductive material 128 isdeposited on the second surface 112 b to act as an electrode. Thetransparent conductive material 128 may be any material which bonds wellto front element 112, is resistant to corrosion to any materials withinthe electrochromic device, resistant to corrosion by the atmosphere, hasminimal diffuse or specular reflectance, high light transmission, nearneutral coloration, and good electrical conductance.

In the present example, the transparent conductive material 128 includesan insulator 131 proximate the second surface 112 b, a metal layer 133,and an insulator layer 135 proximate the electrochromic medium 126,which cooperate to form an insulator/metal/insulator (IMI) stack 139. Ifdesired, an optional layer or layers of a color suppression material 130may be deposited between the transparent conductive material 128 and thesecond surface 112 b to suppress the reflection of any unwanted portionsof the electromagnetic spectrum. Further, a barrier layer 137 may alsobe incorporated, as discussed below. The materials utilized to constructthe insulator/metal/insulator stack are selected to optimize optical andphysical properties of the electrochromic element such as reflectivity,color, electrical switch stability and environmental durability.

While the general concept of utilizing an insulator/metal/insulatorstack within electrochromic mirror application has been disclosed inU.S. Pat. Nos. 5,239,406; 5,523,877; 5,724,187; 5,818,625; and5,864,419, these fail to teach specific stack instructions to attainvarious required properties in order to create a functional and durableelectrochromic device utilizing an insulator/metal/insulator transparentelectrode.

The description herein details the requirements and properties ofnecessary for creating the present inventive and useful IMI stack 139.The particular construction of the present inventive IMI stack 139overcomes many previous shortcomings and problems associated withutilizing an IMI stack within an electrochromic element. Specifically,it has been determined that IMI coatings behave differently inelectrochromic elements as compared to single layer transparentconducting oxides (TCO) when considering visible light transmittance.The reflectivity of a mirror or the transmittance of a window isdirectly dependent upon the absorption of the glass coated with atransparent electrode, with the reflectivity of the mirror or windowbeing reduced when the transparent electrode exhibits substantialabsorption. If the transmittance of the transparent electrode is low dueto reflection losses then a window made with such a transparentelectrode will have a low transmittance and potentially unacceptablereflectivity. The transmittance of a TCO will increase when placed incontact with an electrochromic medium with a refractive index higherthan air, resulting in a drop in reflectance as well leaving the coatedglass with approximately the same absorption. As a result, if a TCO wasused in a window the resultant reflectivity will drop and thetransmittance will increase relative to the parts in air. However, IMIcoatings generally do not behave in this manner. The transmittance of anIMI coating may increase, decrease or stay the same when placed incontact with an electrochromic medium compared to when the IMI coatingis in contact with air. Therefore, proper IMI coating constructioncannot be generalized and the associated behavior within electrochromicapplications calculated as can be done with respect to TCO coatings. Thepresent inventive electrochromic elements incorporate IMI coatingsexhibiting a relative high transmittance and low sheet resistancesuitable for electrochromic applications. Particularly, the behavior ofthe coatings as described work exceptionally well within anelectrochromic cell as compared to air as virtually all prior artIMI-type coatings have been previously described.

As an example, FIG. 5 illustrates the different transmittance of an ITOon glass when the incident medium is air or an electrochromic fluid. Inthis case, the electrochromic fluid is predominantly composed ofpropylene carbonate with a refractive index of 1.44 at 550 nm. Thedominant reason for the change in transmittance is due to a reduction inthe reflectivity. The electrochromic fluid case actually has slightlyhigher absorption (0.2%) as compared to the air case. However, thechange in transmittance between air as compared to electrochromic fluidis not straightforward. An analysis of an IMI stack consisting of glass,a dielectric with an index of 2.0, a silver layer and a top layer alsowith a refractive index of 2.0 was performed, with the thickness of eachdielectric and the silver layers being varied. The change intransmittance between air and the electrochromic fluid was calculated(electrochromic fluid minus air) and the results were statisticallyanalyzed to determine the trends. FIG. 6 illustrates the complexrelationships that exist as relatively simple three-layer IMI stack. Ineach of the contour plots as shown in FIG. 6, two of the layers werevaried while the other layer was held constant.

The particular components utilized to construct the present inventiveIMI stack 139 assist in increasing the transmittance of the stack, withthe refractive index of dieletric layers generally being held as high aspossible. The relatively high refractive indices assist in increasingthe transmittance of the stack 139 with an appreciable thick silver orsilver alloy layer. The need for higher refractive indices for thedielectrics is more critical when the IMI coating is positionedproximate to a relatively high index electrochromic fluid as compared towhen this same coating would be placed next to air. The higherrefractive indices also assists in attaining a range of colors atrelatively high transmittance levels. Preferably, the refractive indicesof the dielectric layers are greater than 1.7, more preferably greaterthan 2.0 and most preferably greater than 2.5.

Table 4 lists the transmittance of a number of stacks that demonstratethe transmittance of the IMI stacks with different dielectric refractiveindices and silver thicknesses. The values were calculated with a thinfilm computer program (TFCalc) as available from Software Spectrum,Inc., of Portland, Oreg. As noted in Table 4, silver thickness was fixedand the dielectrics were optimized to maximize the transmittance. Thethickness of the layers in Table 2 are in angstroms. Specifically,dielectrics exhibiting four different refractive indices were used inthe models, including titanium oxide, (with two different refractiveindices) indium zinc oxide (IZO) and a mixed titanium silicon ixoidelayer. The titanium dioxide may be doped to increase the electrical bulkresistance. The transmittance is shown with air and electrochromic fluidlocated proximate to the IMI stack. It is noted that the higherrefractive indices provide higher transmittance values and that thesehigh transmittance values are maintained with thicker silver layers,thereby allowing relatively high transparency in a window or highreflectivity in a mirror at lower sheet resistance values. As a result,faster switching times are obtained for the associated electrochromicelement. The ability to obtain higher refractive index dielectrics tomaintain a high transmittance over a broad range of silver thicknessesalso indicates the room to adjust the layers for other attributes suchas reflected or transmitted color. The thickness of the dielectrics mayalso be thinner when the refractive index is higher, thereby translatinginto a more economical product as well as a more versatile stack.Preferably, the transmittance to be greater than about 50%, morepreferably above about 60%, even more preferably above 70%, even morepreferably above 80% and most preferably above 90%. If hightransmittance is the principle design criteria, the silver layer ispreferably less than 300 angstroms in thickness, more preferably lessthan 200 angstroms, even more preferably less than 150 angstroms, andmost preferably less than 100 angstroms.

TABLE 4 Transmittance values for different IMI stacks Glass TiO2High AgTiO2High PC TiO2/Air TiO2/PC Index 377 50 368 81.4 89.0 2.8 345 75 33782.6 90.0 312 100 303 84.7 91.0 274 125 265 87.0 91.3 252 150 269 89.190.2 257 175 274 89.2 87.2 268 200 272 87.2 82.6 Glass TiO2 Ag TiO2 PCTiO2/Air TiO2/PC Index 408 50 404 84.4 91.1 2.4 372 75 363 85.7 91.7 331100 317 87.5 92.0 299 125 300 89.7 91.3 302 150 310 90.3 88.6 311 175313 88.7 84.1 316 200 317 84.9 78.0 Glass IZO Ag IZO PC IZO/Air IZO/PCIndex 439 50 416 87.6 91.0 2   419 75 428 89.2 89.3 442 100 444 88.384.9 445 125 445 84.9 78.8 441 150 442 79.5 71.4 Glass TiSi2O6 AgTiSi2O6 PC TiSi2O6/Air TiSi2O6/PC Index 563 25 445 91.5 93.9 1.7 561 50548 92.5 90.8 567 75 559 90.0 84.8 551 100 547 85.1 76.9 542 125 53978.1 68.0 543 150 537 69.7 58.9

In addition to the real part of the refractive indices for thedielectrics the imaginary component of the refractive index of thedielectrics is addressed. The imaginary part of the refractive indexaffects the absorption of light in the dielectric layers. The dielectriclayers of the IMI stack act to minimize the standing electrical field ofthe light in the metal layer, thereby enhancing the electrical field inthe dielectric layers. The magnitude of the absorption due to theimaginary part of the refractive index is therefore increased relativeto what would be seen in the dielectric layer alone in a substrate. As aresult, it is important to minimize the amount of absorption in thedielectric layers to maximize the transmittance of the transparentelectrode. Conversely, the absorption in the dielectric layers may beused to tune the transmittance of an IMI stack without the need toadjust the metal layer which may be fixed for other optical orelectrical requirements.

Table 5 shows the effect of absorption in the IMI dielectric on theattainable transmittance for a fixed refractive index of the dielectric.Thin film modeling was again used to calculate the transmittance andreflectance for IMI stacks with different dielectric layers withapproximately the same real refractive index, n. The silver thicknesswas fixed at 100 angstroms and the dielectric layers were allowed tomove during the transmittance optimization. The maximum transmittance ishighly correlated to the k value in the dielectric. This data was fitwith a linear curve to generate an equation linking transmittance to kvalue in the dielectric. The transmittance versus k values based on thisequation are shown in Table 6. In order to obtain a transmittancegreater than 50%, the k value is preferably less than about 0.2, morepreferably less than 0.1, even more preferably less than 0.04, even morepreferably less than 0.01 and most preferably less than 0.005. At themost preferable level and below there is little change in transmittancewith changing k value. These preferred ranges were determined utilizinga fixed real index for the layers at 2.0. The preferred values for k mayshift slightly when other real refractive indices are used.

TABLE 5 Effect of absorption (k) on the maximum attainable transmittanceand lowest absorption for a fixed n value. Dielectric n k R T A ITO cold2.025 8.61E−04 7.70 88.06 4.24 SiN 2 2.026 1.18E−03 7.61 88.12 4.27 AZO1.975 5.41E−03 8.81 85.64 5.55 IZO 2.016 1.04E−02 7.95 85.62 6.43 SiN 12.120 1.30E−02 6.01 87.32 6.67 SiN 3 2.000 2.30E−02 8.26 82.84 8.90 SiN5 2.000 2.82E−02 8.30 81.99 9.71 SiN 6 2.000 3.89E−02 8.51 80.16 11.33SiN 4 2.000 4.97E−02 9.01 78.34 12.65

TABLE 6 Transmittance versus k value using equation based on values fromTable 4. Estimated k Transmittance 1.00E−05 88.0 5.00E−05 88.0 1.00E−0488.0 5.00E−04 87.9 1.00E−03 87.8 2.00E−03 87.6 3.00E−03 87.4 4.00E−0387.2 5.00E−03 87.0 1.00E−02 86.0 2.00E−02 84.0 3.00E−02 82.0 4.00E−0280.0 5.00E−02 78.0 6.00E−02 76.0 7.00E−02 74.0 8.00E−02 72.0 9.00E−0270.0 1.00E−01 68.0 1.10E−01 66.0 1.20E−01 64.0 1.30E−01 62.0 1.40E−0160.0 1.50E−01 58.0 1.60E−01 56.0 1.70E−01 54.0 1.80E−01 52.0 1.90E−0150.0 2.00E−01 48.0

It is noted that in some applications, it may be advantageous for onlypart of a dielectric layer to exhibit a high refractive index, therebyobtaining optical advantages, such as reflected and transmitted colortuning that would benefit from a combination of indices, or a gradientindex in the dielectric layer.

Another approached to maximizing transmittance in the silver layer(s)within the IMI stack 139 is to create the silver layers with as low arefractive index (real portion) as possible. This relatively lowrefractive index can be obtained via several means. Depositing thesilver layers upon zinc oxide will assist in producing silver with arelatively low refractive index, due to a crystal match between zincoxide and silver. Specifically, the silver is grown pseudo epitaxiallyand has a dense structure, while the zinc oxide layer typically has acrystalline structure when deposited via sputtering. The zinc oxidelayer therefore has the propensity to develop a rough surface due to itscrystalline nature. The thickness of the zinc oxide layer in the stackmust therefore be controlled such that the roughness which often scaleswith the thickness does not become overly large. Further, depositionparameters for the zinc oxide may be used to control the layermorphology and minimize the thickness at various overall thicknesslevels.

The refractive index of silver is also related to its electricalproperties. For a given silver coating the preferred layer will have alow bulk resistance, thereby resulting in higher transmittance values.Two ways are employed to reduce the bulk resistance of the coating,including increasing the electron carrier concentration, and increasingthe electron mobility. The resulting IM stacks has a highertransmittance due to an increase in the electron mobility.

In addition to the electrical properties of the silver layer the d-bandelectrical transitions also affect the properties of the silver layer.In silver, as with most transition metals, electrons may be excited tohigher energy levels, wherein transitions occur in the d-band or dorbitals in the metals. These transitions significantly affect therefractive index of the metals. By altering the electron concentrationin the metal, the frequency at which the onset of absorption may occurwas changed. This was attained by shifting the d-band transitions tohigher frequencies thus lower the refractive index of the associatedsilver layer in the visible region and thus increasing thetransmittance. Preferably the real part of the Ag refractive index in atleast one portion of the visible spectrum between 380 and 780 nm shouldbe less than about 0.12, more preferably less than about 0.10, even morepreferably less than about 0.08 and most preferably less than about0.06.

The interfaces between the silver and the neighboring materialsdramatically affect the final transmittance (and sheet resistance) ofthe IMI stack. Low absorption within the IMI stack occurs as theroughness of the interfaces decreases, or mixing between the silver andthe dielectric increases, with the absorption at a maximum when thelayers are atomically smooth. The materials for the IMI stack anddeposition were selected to provide smooth layers and interfaces.Further, as the roughness of the interfaces increase, the opticalconstants of the silver, particularly the electron mobility, decreases,thus affecting the transmittance in a negative manner. Preferably thepeak to valley roughness of the surface of the layer(s) below the Ag ormetal layer is less than about 50 angstroms, more preferably less thanabout 30 angstroms, even more preferably less than about 15 angstromsand most preferably less than about 10 angstroms. Ideally, the processsettings for the various layers beneath the Ag or metal layer can beadjusted by altering the deposition process settings or method. In thecase where this is not feasible in one embodiment the layers may besmoothed by ion beam techniques to provide the needed surface roughness.

Further considerations were made regarding the selection of materialsplaced next to the silver layer(s). Even with optically smoothinterfaces there exist interface states known as surface plasmons. Thesurface plasmons act as normal layers and do not significantly affectthe reflection properties of the stack but dramatically affect thetransmittance intensity. The frequency, or peak absorption of theplasmons, is a function of the dielectric function of the neighboringmaterials and on the plasma frequency of the silver layer. Therefore,benefits were obtained by appropriate material choices independent ofthe apparent properties seen in thin film models. Ideally, the plasmafrequency of the silver layer should to be as high as possible, with thelayers located adjacent to the silver layer having dielectric constantsselected such that the frequency of the surface plasmons do not lead toappreciable absorption in the coating.

In some applications, a lower transmittance within an electrochromicmirror or window is desired, while maintaining acceptable color,reflectance and low sheet resistance. As an example, utilizing a metalsuch as silver for the reflector, it is possible to modify thetransmittance of an IMI coating to lower the reflectance of the mirrorto meet market requirements. In these cases, introduction of materialsinto the IMI stack to create surface plasmon layers would result incontrolled absorption in the visible region. In this manner, thetransmittance of the IMI coating is tuned while maintaining preferredproperties in other areas. Other means, such as placing barrier or seedlayers adjacent to the silver layer may be utilized. In this manner,thin metal layers adjacent to the silver will lead to lowertransmittance values, and may be used to assist in tuning thetransmitted color.

Other means are available to increase the transmittance of IMI typecoatings. As noted above the refractive index of the silver or metallayer is critical to attaining high transmittance values. Postdeposition annealing of a coating is another means to increase thetransmittance. By heating the sample at elevated temperatures for agiven period of time the transmittance of the coating can be increasedwhile simultaneously reducing the sheet resistance of the coating. Atime-temperature study was conducted on a five layer IMI stack. Thestack consisted of glass/IZO/AZO/Ag/AZO/IZO wherein IZO is indium zincoxide with a percentage of zinc between about 1 and 99 percent and AZOis aluminum doped zinc oxide wherein the doping level of the aluminum isbetween about 0.25% and 10%. The AZO layers were approximately 50angstroms thick, while the silver thickness was about 80 angstroms thickand the IZO layers were approximately 440 angstroms. The stacks wereheated at three different temperatures and for various times. FIG. 7illustrates the results of the change in transmittance with heatingconditions, while FIG. 8 illustrates the change in sheet resistance forthe same heating conditions. As is illustrated, improved IMI stacks arecreated with post deposition heat treatment. Other metals can, ofcourse, be used in replacement of silver, with the preferred metalsshould have a low refractive index to allow appropriate admittancematching of the metal to occur. Preferred metals include silver, gold,copper, aluminum zinc, magnesium, beryllium, cadmium, zirconium, andvanadium. Preferably the coatings are heated between about 150 and 450C,more preferably between 200 and 400C and most preferably between 250 and350C. Preferably the heating time should be between 5 and 40 minutes,more preferably between 5 and 20 minutes and most preferably between 10and 20 minutes.

The color of the electrochromic window or mirror is a critical aestheticcharacteristic, with color neutrality being preferred in manyapplications. For example, modern architectural windows are designed tohave a high “color rendering index” (CRI) wherein the color of objectsis not altered by viewing through a transparency, with a color renderingindex of 100 being a perfect situation and values above 80 beingacceptable, values above 90 being preferred, and values above 95 beingmore preferred. The color rendering index is defined in the followingreference document “CIE Publication 13.3. Method of measuring &specifying colour rendering properties of light sources. CIE, 1995”. Thereflected color of a mirror changes when the mirror is transitioned tothe darkened state. When the mirror is fully darkened, the observedcolor and reflectivity are due essentially from the first and secondsurfaces of the top surface of the glass. U.S. Pat. No. 6,816,297entitled ELECTROCHROMIC MIRROR HAVING A SELF-CLEANING HYDROPHILICCOATING, issued Nov. 9, 2004, and U.S. Pat. No. 6,020,987, entitledELECTROCHROMIC MEDIUM CAPABLE OF PRODUCING A PRE-SELECTED COLOR, issuedFeb. 1, 2000, each commonly assigned with the present invention andincorporated herein by reference, detail how coatings on the firstsurface of the glass and the fluid color affect the appearance of acolor from the bright (un-darkened state) to the fully dark state.

When the mirror is in a fully darkened state, with zero light from thereflector on either the third surface or the fourth surface reaching theobserver, the appearance of the mirror is due to a combination of lightfrom the first and second surfaces of the first substrate. With nocoating on the first surface, about 4% reflectance from the uncoatedglass interface is obtained, with any color due to thin filminterference effects from the transparent electrode on the secondsurface. The color of the transparent conducting oxide is due primarilyfrom the thickness of the layer. As the thickness of the TCO isincreased, the color changes in a predictable manner. The color can befurther altered by adding additional layers either above or below theTCO. The above-referenced patents teach methods for minimizing the colorof TCO and other coatings. The reflectance of the mirror in the darkstate is also affected by the thickness of the TCO and whether otherlayers are present in the coating stack. As a result of the absorptionin ITOs or other TCOs being fairly low, there is little color change inthe bright state of the mirror due to thickness changes in the layer.Similarly, in a window the ITO does not contribute substantially to thetransmitted color nor is color tuning by adjusting the ITO an option.

In order not to affect the inherent color of the reflecting metal layerof the electrochromic mirror, an IMI transparent electrode must have atransmitted color rendering index greater than 80, preferably greaterthan 90 and most preferably greater than 95. Unlike a window, the lightfalling on a mirror must pass through the coating twice, the first asthe light approaches the reflector and the second time after the lightreflects off of the reflector. If the color rendering index of the IMIcoated glass is too low then the color of the reflector is altered. Inmany electrochromic mirror applications, the mirror must be fairlyneutral. Low color purity levels are preferred whereby the hue of theimage is not substantially altered by the mirror. It is noted that notall IMI stacks inherently have sufficiently high color renderingindices. The refractive indices of the dielectric layers and thethicknesses of all the layers work in concert to yield a finaltransmitted color, with the color changing as the layers are altered. Inmany cases, the need for acceptable transmitted color conflicts with theneed for maximum transmittance, with the optimization for hightransmittance causing the transmittance spectra to shift from neutralityleading to a colored transmittance. Specifically, as discussed in termsof a* and b*, a negative a* will be obtained with relatively hightransmittance coatings due to the biased response of the human eyetoward green light. In order to obtain a positive a* a lower cap Y forthe same average reflectance level must be maintained, which in mostapplications is not preferred. As a result of having a negative a* forhigh transmittance applications, the major difference in color is ashift is expected in a shift in b*. The hue therefore shifts between ayellow bias and a blue bias. As a result, the IMI stack is properlydesigned so that the color does not shift outside of a particular rangefor b*. Preferably the color shift of the reflector is less than about10 C* units where C*=sqrt[sqr(a*)+sqr(b*)], more preferably less thanabout 5, most preferably less than about 2.5. Alternately, preferablythe color shift of the reflector is less than about 10 b* units, morepreferably less than about 5 b* units and most preferably less thanabout 2.5 b* units. In many applications, the reflector exhibits a colorbias that is objectionable, thereby forcing designers to discard theparticular reflector for the intended application. With the new abilityto tune the transmitted color of the IMI coating, the final color of themirror may be rendered acceptable by adjusting the color of the IMIcoating to compensate for inadequacies in the reflector. In this mannerthe range of acceptable materials for the reflector is increased whichmay bring other benefits to the final mirror assembly. For example, acommon problem with various reflectors is a yellow color bias, resultingin a yellow appearance of images in the final mirror assembly. However,the final mirror color may be made more blue by altering the IMI coatingwith the IMI coating being designed to yield a preferential bluetransmitted color which would therefore transmit relatively less yellowcolor. The amount of blue shift is based on the relative transmittanceof blue and yellow light through the IMI and can be approximated by theb* color value. Preferably the color correction of the reflector by theIMI coating is greater than about 2.5 C* units, more preferably greaterthan about 5, most preferably greater than about 10. Alternately,preferably the color shift of the reflector is greater than about 2.5 b*units, more preferably greater than about 5 b* units and most preferablygreater than about 10 b* units.

The reflected color, as mentioned above, is also critical for anelectrochromic mirror applications. In the darkened state, the colorviewed by the observer is dominated by the color of the transparentelectrode on the number second surface, with thicknesses and refractiveindices of the layers affect the final color of the product. In additionto the thickness of the layers, the color can be tuned by selectingdielectrics with absorption at different wavelength bands. Typically,common dielectrics will have absorption in the blue part of thespectrum, while other dielectrics may have absorption in other bands ofthe visible spectrum. The dielectric materials may be selected based ontheir absorption properties to yield the desired final color propertiesof the IMI stack and final mirror. The color can also be tuned by havingdielectric materials in the stack with different refractive indices. Thechange in index of the dielectric layers may be used to help attaindifferent combinations of reflectance, transmittance and color notattainable with IMI coating consisting of only a fixed refractive indexfor the dielectric layers.

The color in the intermediate darkened states is also often important inelectrochromic mirrors. The change in color as the mirror darkens isreferred to as the color excursion. The mirror is often set tointermediate states of darkening and the reflected color is acombination of the color of the fluid, the color of the reflector andthe color of the transparent electrode. The IMI coating should yield anacceptable color in the intermediate darkened states. Preferably thedark state reflected color has a C* value less than about 35, preferablyless than about 20, more preferably less than about 10 and mostpreferably less than about 5.

In many applications the color at oblique viewing angles is criticallyimportant. In particular, for window applications it is often necessaryto have a pleasing color at all or most viewing angles. Specific layers,thicknesses and refractive indices, are needed to attain this goal. SomeIMI stacks are more susceptible than others to changes in color withangle. The thickness of the silver layer and the thickness of thedielectric layers have been shown to be critical for acceptableperformance in an electrochromic element. The thickness of the silverlayer should preferably range from about 50 angstroms and 500 angstroms,more preferably range from about 75 and to about 250 angstroms, and mostpreferably range from about 100 and 150 angstroms. The total thicknessof the top and bottom dielectric layers will vary between about 100angstroms and 700 angstroms. Thicker layers may some times be used ifspecific color objectives are needed. The thickness of the dielectriclayers above and below the metal layer may be divided among manydifferent dielectric materials which may be added to the stack toprovide particular chemical, physical, and/or environmental durabilityrequirements as described below. Preferably the reflected color shiftsin going from normal incidence to 45 degrees less than about 20 C*units, more preferably less than 10 and most preferably less than 5.

In many cases it is difficult to meet all aesthetic, electrical andenvironmental requirements with an IMI stack which contains only asingle metal layer. This is overcome by designing IMI stacks whichconsist of multiple metal layers. By making a stack with two or moremetal layers, more degrees of freedom are allowed for more combinationsof transmittance and reflected colors and intensities. The multiplemetal layers also allow for a lower sheet resistance for the IMI coatingwhich translates into faster switching time for the electrochromicwindow or mirror. Typically, a two metal layer stack would have arelatively thin base layer, a metal layer, a relatively thick centerdielectric layer, a second metal layer and a relatively thin topdielectric layer. The thicknesses of the dielectric layers is relativeto the other dielectric layers. The metal layers are typically thinnerthan the dielectric layers. The dielectric layers may comprise differentmaterials to attain certain design goals similar to what has beendescribed for single metal IMI coatings. The selection of dielectricmaterials and metals and their thicknesses are based on the particulardesign goals. For example, if a higher transmittance is critical thenthe metal layers tend to be thinner while if a low sheet resistance isthe critical design goal then the metal layers may be thicker. The useof multiple metal layers in an IMI coating may often help attain highertransmittance at a given sheet resistance level. Further, multiple metallayers may provide uniform color at oblique viewing angles relative tosingle metal IMI stacks.

As is know in the art, ultraviolet shielding and solar shield is arequirement of electrochromic windows. Typically, these windows use acomplicated series of glass panes and coatings to achieve the propershielding. However, prior attempts at designing electrochromic windowsthat exhibit the necessary shielding properties fail to disclose the usethe use of IMI coatings therein. Instead, past attempts have taughtutilizing additional coatings on glass which are laminated to theelectrochromic window. These additional layers, though functional,necessarily increase the weight of the associated window assembly andthe cost thereof.

UV shielding or blocking may be attained in an IMI transparent electrodethrough a combination of material choices and the optical design of thestack. For example, the dielectric materials may be selected whichdisplay UV absorption properties. Specifically, TiO2, CeO2 and zincoxide are effective UV absorbers. These materials display UV absorptiontypically due to their optical band gap. The absorption of the UV lightby these materials may be augmented by the optical design of thecoating. For instance, the IMI stack may reflect a portion of the UVlight further reducing the overall UV transmittance.

The metal layer of the IMI stack 139 may also have UV blockingproperties. For example, silver has absorption in the UV spectrum due tooptical transition of electrons to the d-band from lower energy bands.These so called d-band transitions result in substantial absorption ofUV light. In the case of silver, the d-band transitions occur atrelatively high energies in the UV part of the spectrum. Other metalssuch as gold and copper have d-band transitions at lower energy states.In the case of these metals, the d-band absorption results insignificant coloring of the metals, however, these metals display betterUV blocking than silver. The properties of silver or other metals may beaugmented by alloying with metals displaying higher UV absorptions,especially if the absorption is due to atomic absorption and not acrystal structure related absorption. Preferably the UV transmittance isless than about 75%, more preferably less than 50%, even more preferablyless than 25% and most preferably less than 15%.

Metals and other electrical conductive materials reflect infrared andsolar radiation. The intensity of the reflected light is proportional tothe electrical conductivity of the material and the thickness of thelayer. As the thickness of the layer or coating is increased, thereflectance asymptotically approaches a maximum value which, to firstorder, is dependent on the conductivity of the material. Materials withhigher conductivity have higher infrared reflectivity. In addition, thereflectivity increases at shorter wavelengths as the conductivity of thematerial is increased. As mentioned above, the origin of theconductivity affects the transmittance and reflectance of a coating. Theconductivity of a material is a combination of the electron density andelectron mobility. Each of these attributes affects the infraredreflectivity in different ways, with the infrared reflectivity beingmaximized when the conductivity is due to high electron density ratherthan high electron mobility.

The solar transmittance and reflectance may also be adjusted by theoptical design of the IMI coating. For instance, multi-metal layerstacks may have a higher rejection of solar light than single metallayer stacks. The solar rejection properties of an electrochromic windowcan be further modified if additional layers are added to the first andfourth surfaces. These additional coatings can give low e benefitsand/or may provide additional solar screening properties. Furthermore,the electrochromic window may be combined with another pane or panes ofglass into an insulated glass configuration. The additional panes ofglass may be uncoated or coated with layers to provide specific UV orsolar rejection properties. To minimize solar heat gain (SHGC), theelectrochromic window should be placed such that it is the first lite tothe outside and a low e coating is placed on the fourth surface.Additional layers may be added on the surfaces of the glass panes asaesthetics or functionality require. In general, the use of an IMI layerin an electrochromic window will reject substantially more solarradiation at a given ohm/sq as compared to a transparent conductingoxide. Moreover, the IMI layer can accomplish this at a much reducedcost. In the bright state the SHGC is preferably less than about 0.7,more preferably less than about 0.5, most preferably less than 0.3. Inthe dark state the SHGC is less than about 0.5, more preferably lessthan about 0.3 and most preferably less than about 0.15.

Traditionally, dielectric layers in IMI coatings fall into two disparatecategories. In architectural window applications the dielectric layersare typically non-conductive and, historically, transparent conductingoxides have been avoided due to the high cost of the materials and themanufacturing complexity which are typically associated with thesematerials. Often high temperatures or elaborately-controlled processesare needed to attain the optimal light transmittance and conductivityfor the layer. In cases where the IMI coating would be used as atransparent electrode, the dielectric layers are usually transparentconducting oxide, with the transparent conducting oxides needed to allowelectrical conduction perpendicular to the coating surface. Previousapproaches severely limit the list of viable materials for use in an IMIcoating for an electrochromic application.

The objective of a transparent electrode is to provide electricity to anelectrochromic cell while providing sufficient transparency for a givenapplication. However, additional benefits may be obtained by optimizingthe conductivity of the different associated layers. The electrochromiccell may be treated as a group of resistors in parallel, with the firstresistor as the high conductivity metal layer. The high conductivity ofthe layer allows more electricity to reach the center of the associatedpart rather than traveling perpendicular to the plane of the coatingnear the edge of the cell, which in turn leads to a more even darkeningof the part. The assumption is that there are no appreciable voltagedrops in the direction perpendicular to the metal coating, as istypically the case when using a TCO as the transparent electrode.

When additional layers are added to the top of a metal layer, such as inthe case of an IMI stack, then additional design criteria come arenecessary which may be tailored for additional benefits within theelectrochromic cell. By placing a relatively high conductivity TCO ontop of a metal layer, no appreciable voltage drop perpendicular to themetal layer is introduced. However, if the TCO or other dielectric layerhas relatively low conductivity then an additional voltage drop occursperpendicular to the metal surface thereby limiting the current flow.This additional voltage drop evens out the voltage drop perpendicular tothe surface at the edge of the part compared to the center of theviewing area. The quantitative benefit is a function of many variablessuch as cell spacing, fluid properties, cell size and relativeconductivity of the different materials. The net effect is that incertain applications more uniform darkening may be obtained byintroducing a relatively low conductivity layer between the higherconductivity metal layer and the electrochromic medium.

The issue of necessary conductivity and the location of specific levelsof conductivity are important for IMI coatings constructed of multiplemetal layers. The cost of multiple metal IMI coatings is reduceddramatically if high cost materials such as ITO are not needed in allparts of the IMI stack. For example, in a two silver layer stack thecenter dielectric layer is often up to 700 angstroms or more inthickness and the top and bottom dielectrics can be in excess of 350angstroms, with the total amount of ITO in the stack being about 1400angstroms and thereby introducing a substantial cost to the product. Bysubstituting some or all of the ITO with a material with lessconductivity, the overall performance of the coating is not compromisedbut the cost is reduced dramatically.

The material immediately in contact with the electrochromic medium iscritical to the performance of the electrochromic device. For instance,some materials react with materials in the seal or fluid and passivateall or parts of the surface which results in differences in thedarkening properties of the electrochromic device. Passivation may beminimized by ensuring that the top layer of the IMI coating has certaindesirable properties. One such property is the ability of the layer toconduct electricity. By having the top layer with a resistance of about10 MOhms then the probability of passivation is substantially reduced. Anormally low conductivity layer may be made viable as the top layer nextto the electrochromic medium by altering the composition through dopingor stoichiometry to introduce a level of conductivity sufficient toreduce the passivation. Other chemical means may be employed to renderan incompatible material viable by altering the surface chemistry of thelayer. Appropriate application of chemical ligands or moieties cansufficiently alter the surface properties to minimize the potential forpassivations.

The dielectric layer under the metal layer may be a TCO, however, it isnot required. The overall conductivity of the IMI stack is notsubstantially improved if the base layer is not a TCO due to thesubstantially higher conductivity of the metal layer. Other preferredmaterials for the dielectric layer due to the increased conductivity ofthe metal layer include: ITO, IZO, AZO, ZnO, TiOx, CeOx, SnO2, SiN,SiO2, ZnS, NiOx, CrOx, NbOx, and ZrOx. The materials may be pure,stoichiometric or partially stoichiometric, doped or mixed with oneanother to provide intermediate properties. Preferably, if transmittanceis to be optimized, materials should be avoided that display appreciableabsorption. The absorbing materials may be preferred in cases where thematerials have a relatively high refractive index and the absorption inthe layer augments the reflectance and transmittance properties of thethin film interference optics and results in attributes which would notbe practically attainable without the absorption. Other conductiveoxides, sometimes used as electrochromic layers, which when capped withadditional layers would not appreciably darken might also function aspart of the IMI stack. These layers may be acceptable and may notrequire to be capped even if the layers darken slightly with the appliedelectric field. Materials such as WO3, NiO or IrO2 would fall in thiscategory.

The layer immediately above and more importantly below the metal layeris critical to the overall properties of the IMI stack. As discussedabove, certain materials may have effects on the transmittance andelectrical properties of the stack. The layers adjacent to the metallayers also affect the adhesion of the metal layers to the dielectriclayers. The barrier layer above the metal layer also may play a role ofprotecting the metal layer from the effects of deposition process of thesubsequent dielectric layer. The top barrier layer is often thought of,therefore, as a sacrificial layer since it often becomes altered bysubsequent deposition steps.

The structural integrity of the IMI stack may be compromised if theproper base layer or top layer is not used. IMI stacks with goodstructural integrity may be needed if the IMI coating is installedbetween a substrate (such as glass) and the epoxy (or other sealingmethod) sealant in an electrochromic device. The IMI stack thereforeneeds to have good adhesion to the glass and epoxy and also have goodinternal adhesion. The coating may become ineffectual in thisapplication if the adhesion between any of these areas fails. A commonfailure point within an IMI coating often is between the metal layersand the neighboring materials. If this area does not have sufficientadhesion then the electrochromic device may suffer a catastrophicfailure and cease to function. Materials that function well as a barrierlayers to promote acceptable adhesion include, Ru, Ni, NiCr, NiCrOx, ZnO(or doped ZnO), Cu, Ti, Nb, NbOx, Ni, Pd, and Pt. The thickness of theselayers may be adjusted to attain the necessary protective and adhesionproperties. Typically, the thickness of metal layers used in thiscapacity would vary between several angstroms in thickness on the thinside and greater than 20 angstroms or 40 angstroms on the thick side.Preferably the thickness of a metallic barrier layer is between about 1and 40 angstroms, more preferably between about 2 and 20 angstroms andmost preferably between about 3 and 10 angstroms. Oxide, nitrides orother materials with lower absorption could be substantially thickerthan the corresponding metal layers, with the thickness preferably lessthan or equal to about 150 angstroms, more preferably less than or equalto about 100 angstroms, and most preferably less than or equal to about50 angstroms.

The layers next to the metal layers may also affect the performance ofthe metal layers during electrical switching or “cycling”. The potentialat which a metal will break down or go into solution is a function ofthe properties of the electrochromic cell. The neighboring materials tothe metal of the IMI stack effect the maximum attainable potentialdifference before damage to the coating occurs. Typically, noble metalsas neighboring materials will help metals such as silver survive athigher applied switching potentials, and preferably include Au, Ru, Rh,Pd ,Cd, Cu, Ni, Pt, and Ir. Barrier materials may also alter theelectrical potential at which breakdown or de-plating occurs duringelectrical cycling. Preferably a neighboring material or electricalstabilization layer, will increase the viable usable applied electricalpotential of silver or another metal described herein as a viablesubstitute for Ag by about 0.05 volts more preferably it will increasethe usable potential by about 0.10 volts, even more preferably by about0.20 volts, even most preferably above about 0.30 volts. Appropriateselection of the neighboring materials will increase the viable appliedpotential to the cell. The viable potential needed for an IMI stack willchange if the IMI is used as the cathode or the anode.

Another means that may be used to further stabilize the IMI coating tosurvive higher applied potentials includes alloying the metal layer withmetals which themselves can survive higher applied potentials. Forinstance, gold may be doped or alloyed with silver to allow the silverto survive higher applied potentials. Other materials which may beuseful include other noble metals, and preferably include Pd, Si, Ge,Mg, Au, optisils, Ti, or Cu.

In addition to surviving at higher applied voltages, the IMI coatingneeds to survive scratches or other damages without the damage growingwith time or electrical cycling. This may be attained by includingadditives to the metal which will “heal” a defect. For instance, indiumor titanium doping in a silver metal layer may cause a migration toeither the grain boundary or to the interfaces of the silver layer toprevent the silver from agglomerating or becoming further damaged. Thesehealing capabilities may be obtained by doping the silver with elementsor compounds which naturally migrate to the grain boundaries of thematerial or the interfaces.

The stability of IMI stacks, and in particular silver based IMI stacks,is dependent on the properties of the metal layer. Typically, inenvironmentally-harsh conditions typical of accelerated weatheringtests, the coatings break down or degrade at the metal layer. Ideally,the IMI stack would provide a pinhole free coating, however, it isnearly impossible to make a perfect coating in production. As a result,other means are needed to stabilize or protect IMI coatings so thatthese will not break down during the expected use life cycle.

A common degradation mechanism for silver-based IMI coatings is for thesilver layer to re-crystallize or agglomerate forming large low-energystructures. This agglomeration process is caused by the thermodynamicdrive for the silver layer to locate to a low energy state. Thedegradation mechanism can be slowed or stopped by interrupting theprocess by eliminating one or more of the intermediate steps in theoverall degradation mechanism. For instance, the initial energy state ofthe silver layer is a critical factor for whether or not theagglomeration can take place or the rate of formation. If the silverlayer is deposited or subsequent to deposition is put into a stablethermodynamic state by post processing, the IMI will resistagglomeration when subsequently exposed to external stimuli as there isno significant energy drive for the silver layer. The silver can be putinto a lower energy state by several different means. The first is toselect appropriate barrier or base layer materials for the stack suchthat during the deposition process the silver naturally falls into itslow energy state. Zinc oxide as a base layer is particularly well suitedfor this task. Other materials also have benefits and are preferred suchas Sb.

The second is the use of ion beam assisted deposition, while the thirdincludes options such as plasmons, metastables, etc. The treatment ofthe base layer and/or the top of the metal layer before the depositionof the subsequent layers may also modify the surface and thus promoteimproved nucleation and/or adhesion. Chemical means may also be employedto allow the silver layer to be deposited into a lower energy state orto bind the silver layer to the barriers or base layers thus limitingthe silver layer's ability to agglomerate. Preferable metal barriersinclude NiCr and other Ni alloys and noble metals. The pretreatment ofthe dielectric layer or metallic barrier or other neighboring materialwith a sulfur containing compound such as a di-sulfide can substantiallyimprove the nucleation and bonding of an silver metal layer to the baselayer. The enhanced nucleation and improved bonding which results fromthe treatment can substantially improve the stability of the silver ormetal layer thus extending is useable lifetime. Other means may be usedto introduce small amounts of sulfur into appropriate positions in theIMI stack. For instance, small amounts of a sulfur containing gas (suchas H₂S or SO2) may be added to the deposition process. Further, a giventarget may be intentionally doped with appropriate levels of sulfur.This approach has the added benefit of not introducing a highly reactivegas into a deposition chamber, while allowing the amount of sulfur to beeasily controlled. The zinc oxide barrier layer described above may bedoped with a small amount of sulfur to assist in the enhancement ofadhesion of the silver layer to the barrier layer.

In addition to improving the useful life of the parts these means alsohelp the intra-stack adhesion of the layers which comprise the IMIcoating. Improving the intra-stack adhesion allows the stack to be usedin more applications without the need for elaborate masking to protectthe stack from the forces applied by epoxy sealants or other similarstressors.

The stability of the silver or metal layer can also be enhanced by theaddition of dopants to the metal layer. In the case of silver, thediffusion of the silver atoms is approximately 100 times faster alongthe surface grain boundaries than in the bulk metal crystallites. It isexpected therefore that the main pathway for agglomeration occurs due tosilver atom diffusion along the surface or grain boundaries. Thelikelihood that diffusion will occur across the surfaces will be reducedwhen the silver is sandwiched between layers. The selection ofappropriate materials or chemical treatments to the neighboringmaterials next to the metal layer will further reduce the likelihood ofsurface related diffusion and agglomeration. The grain boundaries thenbecome the dominant pathway for the silver layer to agglomerate. Thediffusion along the grain boundaries can be impeded by doping the silverwith elements or compounds which have limited solubility in the silvergrains and migrate to the grain boundary. These dopants limit thediffusion of the silver atoms along the grain boundaries, and preferablyinclude Pd, Cu, In, Zn or Ti.

Another factor which that affects the agglomeration of silver and othermetals is the adhesion of the metal to the neighboring metals. Whilepreferred metals and materials were discussed above, certainapplications may render these previously acceptable materialsunacceptable. Certain elements such as Na, Mg, Ca or other constituentsfound in glass substrates can cause adhesion problems between the silveror other metal layer and the neighboring materials. These elementsaffect the adhesion of the silver layer and thus weaken one of the linkspreventing or stabilizing the silver layer to agglomeration. Theseelements often diffuse from the substrate under high temperature andhigh humidity conditions or during thermal processing of the coatedglass, and can diffuse from the substrate more slowly under normaloperation conditions thereby resulting in so-called latent defects.

The amount of Na that may diffuse from the substrate is affected by thepresence of elemental hydrogen or protons in the coatings stack. Thesodium in the glass as a positive ion and in order to maintain chargeneutrality, a counter ion must move into the glass matrix. The protonacts in this capacity. Therefore, it is critical that hydrogen isminimized in the coating. This may be accomplished by operating thedeposition process in a manner to minimize the hydrogen or water contentwithin the associated processing machinery. It is critical to minimizethe water along with the hydrogen due to the fact that the water iseasily broken down in the plasmas to liberate the hydrogen. The waterand hydrogen may be minimized by the appropriate selection of pumps inthe process and the use of water traps such as polycolds. Careful leakdetection and elimination are also important.

Another way to minimize the impact of sodium and other glassconstituents on the breakdown of an IMI coating include the use of abarrier layer. Typically, barrier layers are principally composed ofsilica and are deposited directly onto the glass substrate due to theclose match in refractive indices. Dopants are often added to the silicabarrier layer to help promote the blocking of elemental transfer.Materials such as phosphorus doped silica and aluminum phosphate mayalso be used.

It is important that barrier layers are amorphous in nature. Crystallinelayers, with their numerous grain boundaries, typically are lesseffective in blocking the transfer of small elements. Further, thebarrier layer does not need to be directly deposited onto the glass, andbe integrated into the IMI stack as a function or optical layer andsimultaneously play the role of a barrier layer. Silicon nitride andzinc stannate are particularly effective barrier layer materials. Theefficiency of the silicon nitride for blocking the diffusion of elementsmay be improved by altering the composition of the silicon nitride bymaking the silicon nitride slightly silicon rich, thereby enhancing thesodium blocking properties of the layer.

The benefits of using an amorphous layer below the metal may also beapplied to the layer above the metal. The top dielectric may be designedso that some or the entire layer is composed of an amorphous layer. Theamorphous layer limits the diffusion of environmental moisture or otherchemicals down to the IMI stack, thus extending the lifetime thereof.

The stress level in dielectric and/or the metal or silver layer alsoaffects the lifetime of the IMI stack, as the stress in the materialscreates different types of forces on the metal layers. For instance, ifthe layer above the silver layer is in compressive stress then it puts avertically oriented force upon the metal. This force may then accelerateor enhance any inherent drive for the metals to agglomerate. Thepreferred state, from a stress standpoint, is when the metals anddielectrics are at comparable stress states, either both tensile or bothcompressive. The magnitude of the driving force the stress exerts on themetals dictates how significant an issue the stress becomes on thelifetime of the IMI stack. A preferred level of absolute stress for thedialetric layer is below 3 GPa, more preferably below 1.5, and mostpreferably below 0.5. The stress in the materials is usually a functionof the material properties but are also dependent on the processparameters used to deposit the layers. If MSVD techniques are used todeposit the layers then the pressure is a key variable for adjusting thestress level in the coating. High stress levels promote tensile stressconditions while low pressure promotes compressive stresses. The ratioof the sputtered atom to the sputtering gas atomic masses also plays arole in the final stress in the coatings. A higher mass in thesputtering gas will promote more tensile stress while a lower mass willpromote more compressive stresses. Dopants or low level additives canalso be used to help tailor the stress levels in the layers. It is anadvantage for one or more of the layers to be deposited with differentsputtering gasses or pressures to attain the necessary stress levels.Ion beam assisted deposition or other means to provide energy to thesystem may be used to help tailor the stress levels in the differentlayers.

Construction IMI coatings with essentially neutral stress profiles havethe added benefit of not distorting the glass or substrate. The internalstress in the coatings, inherent during the deposition process or due todifferences in the coefficient of thermal expansion, exert forces on thesubstrate thus causing warping or deflection in the substrate. In mirroror window applications, where flatness and uniform cell spacing arecritical features of the product, then deflection of the substrates dueto stresses in the coatings can be very problematic. The IMI coatingswith neutralized stresses help minimize the warping issue thus resultingin an overall superior product. As substrates are thinned for weightsavings the amount of deflection for a given stress level increases.Therefore, the issue is exacerbated under these conditions and the needfor a stress neutral product is more important. The stress in the IMIshould be controlled such that the change in radius of curvature of theglass with the application of the IMI coating is greater 3000 mm,preferably greater than 5000 mm and most preferably greater than about10,000 mm.

As noted above, the properties of IMI coatings may change with thermalprocessing. Epoxies are typically used to seal two lites of glasstogether to form an electrochromic cell with preferred time andtemperature curing profiles giving rise to optimal epoxy profiles.Certain existing families of profiles yield equivalent epoxy properties.The selection of a given profile is often then based on other criteriasuch as economics, speed of processing or other practical matters.Typically, a TCO based transparent electrode will not significantlychange properties during the thermal processing, thereby providing noreason to select a given furnace profile for curing the epoxy. However,these thermal profiles may be utilized to optimize the properties of anIMI coating. For example, the sheet resistance may be lowered by up to2-3 ohms and the transmittance may be increased by 1-3% depending on thetime temperature profile. In this manner, the IMI properties areimproved to a state not necessarily attainable by adjusting thedeposition properties. The reason for the improved properties isexpected to be due to increases in the electron mobility of theelectrons in the metal. As noted above, metals (silver) have lowerrefractive indices when the electron mobility is relatively large withthe lower refractive index contributing to the higher lighttransmittance, and the higher electron mobility also then contributes tothe lower sheet resistance.

If the epoxy cure-profile cannot be adjusted to fully optimize the IMIproperties because of limitation in the epoxy or in other components ofthe electrochromic cell then the IMI coated glass can be pretreated in adifferent furnace or oven to attain the desired properties. The thermalprocessing of the IMI may also have the beneficial property of havinglower stress levels, thereby keeping the glass relatively flat. Theoptimal increase in transmittance and decrease in sheet resistance isoften a function of the ambient atmosphere. Typically, the coating maybreak down at earlier times or at lower temperatures if the preferredgas is not used. The preferred gas is often a function of the dielectriclayers which are used in the IMI stack. Some materials are particularlyeffective at blocking the diffusion of different gasses. Siliconnitride, for example, an amorphous material, is particularly useful atblocking the diffusion of oxygen during the heat treatment of IMIstacks. The base layers and barrier layers discussed above for improvingenvironmental durability also play a role in shifting the thermal curebehavior.

In some cases the method of heating the glass can be selected to alterthe cure profile behavior. For instance, infrared wavelengths can beused which pass through the glass but couple effectively to the IMIcoating. Heating the glass in this method is akin to heating the coatedglass lite from the bottom up. Typically, in a convection oven ortraditional infrared oven the electrochromic cell is heated from theoutside in. The outer surface of the top and bottom glass lite isexposed to the convection gasses and/or the infrared radiation. If theinfrared radiation is peaked at wavelengths greater than about 5 micronswavelength then only the surface of the glass is heated. The glass andepoxy are then heated by conduction from the surface into the bulk. Thecoated surface is the last portion of the part to receive the heat. Whenhotter infrared elements are used to heat the part then the bulk of theinfrared radiation is at wavelength shorter than about 2.5 microns. Asthe glass is quite transparent, the radiation passes through the glasswithout being absorbed. The energy couples to the IMI coating due to itsunique optical properties resulting in the coated surface potentiallyheating up at a faster rate than the outer surface which is actuallycloser to the heat source, thereby reducing the curing time such thatthe bulk temperature of the glass may be reduced in the process. Theepoxy will heat up faster also as it is in direct contact with theepoxy.

The IMI coating may be applied using an online coater such as a rotarycoater or in-line singles coater. These coater types will allow thecoating to be laid up relatively quickly after the deposition hasoccurred. Each of these methods has different options for masking. Thesemethods then allow for using a greater range of materials since thecoatings will not be exposed to the atmosphere for any extended periodsof time. The sealing of the IMI stack in an electrochromic cell can thusprotect it from many harmful environmental stressors. In some cases, anIMI stack is optimized for a given set of criteria resulting in lessthan optimal environmental durability. As noted above, one method todeal with this situation is to mask the IMI coating in board of theepoxy. This is a viable method to deal with the issue. However, someapplications may not allow for masking the IMI in board of the epoxy. Inthis case a protective edge coating, such as a polymer coater, etc.,which can encapsulate the IMI coating thus preventing contact with anyharmful chemicals in the environment is applied.

In other situations it may be advantageous to make the IMI stack inlarge area coaters and store the glass for use at later time onproduction lines which do not have coaters. Methods were discussed aboveon how the IMI stack can be designed to optimize the stack for this typeof manufacturing scenario. For example, a temporary overcoat materialsuch as a low tack plastic sheet or a chemical protective material suchas PVA may be applied. These materials may be either physically removedafter any mechanical process or before washing. In the case of usingwater soluble chemical protective layer such as PVA, the washer itselfmay be utilized as the means of removing the temporary coating. Othertemporary coatings such as Zn metal may be used. In this case, a mildacid may be necessary in the first sections of the washer to remove thelayer. Other treatments as known in the art are also viable.

Certain electrochemical mirror applications may incorporate the hidingof the epoxy seal by applying a reflective layer on the top lite ofglass. The methods and materials useful in such applications aredisclosed in U.S. Patent Application Publication No. 2004/0032638,entitled ELECTROCHROMIC DEVICES WITH THIN BEZEL-COVERED EDGE, filed May6, 2003, which is incorporated herein by reference. The use of an IMIcoating as the transparent electrode in these devices introduces somesignificant changes. For instance, it is not cost effective in someapplications to deposit the reflective metal layers underneath thetransparent electrode. This is because the TCOs such as ITO are used asthe transparent electrode. These materials require high depositiontemperatures to get adequate electrical and optical properties. Theglass, with the reflective metal layer, is to be heated prior to thedeposition of the TCO. The presence of this highly reflective metalaround the edge of the glass substantially changes the heating behaviorof the glass and can therefore introduce distortion into the part.

This problem is avoided if an IMI stack is used as the transparentelectrode. The IMI coatings do not require high deposition temperaturesduring the deposition process. A metal layer or layers may then beapplied prior to the IMI coating without the problems which would beassociated with a TCO layer. If a rotary coater, or other coater capableof multiple masks, is used for the deposition then the metal layer canbe applied to the glass in one (or more) station(s) with one mask thenthe IMI can be applied over the remainder of the glass with anothermask. If necessary, the metal layer can then be masked in board from theepoxy while still maintaining good electrical contact to the edge of thepart.

EXPERIMENTS

A first round of experiments demonstrated that the material next to theAg layer affects the performance of the stack in blow tests, steamlifetime and the aesthetics of the final part. Steam lifetime is anaccelerated test to gauge the stability of seals, coatings orcombinations of these materials (described in more detail below). Thetests showed that aluminum-doped zinc-oxide (AZO) is optimal foradhesion (29 psi and no intra-coating lift) while indium-zinc oxide(IZO) is optimal for steam lifetime (35 days). A second round ofexperiments were designed to build on these results and attained acompromise in steam lifetime but a match to the poorer blow test resultsof round 1 (lack of intra coating adhesion). Blow tests are a means toassess the adhesion of coatings to seals, substrates and intra-coatingadhesion (described in more detail below). An unfilled EC element has ahole drilled in the glass and the chamber is pressurized until failure.The pressure at failure is noted along with the failure mode. Thereflectivity of mirror elements was increased to 79% with optimizedstacks from round 2 experiments. Room temperature electrical cycling ofround 2 parts showed latent defects where scratches or finger printswere initially present.

It is noted that maximum transmittance and minimum resistance in wasattained with IZO base layers and AZO top layers; that AZO/Ag/AZO stackprovided maximum intra-coating adhesion and did not unzip in blow tests;that IZO directly on top of the Ag layer had poor adhesion; that stackswith IZO top layers have good stability in steam tests while the stackswith AZO top layer had poor performance in steam tests; and that thecosmetics with IZO top layer were improved.

In the first round of experiments silver was used in combination withaluminum-doped zinc oxide (AZO) and indium-zinc oxide (IZO) to produce 3layer IMI stacks for evaluation. The AZO target used was ZnO containing2% Al₂O₃ by weight. The IZO target used was In₂O₃ containing 15% ZnO byweight. AZO is a transparent conductive oxide similar to ITO but withsomewhat lower conductivity. Like ITO, AZO requires significantsubstrate temperature during deposition to maximize crystallinity anddevelop optimum electrical properties. AZO has the unique property oflattice matching to Ag. This leads to IMI stacks with lower sheetresistance and higher transmittance. IZO, in contrast, is an amorphousmaterial and can be deposited at room temperature without a loss ofconductivity. The amorphous nature of IZO gives it the added benefit ofsmoothness. The IZO composition can vary from almost 100% zinc contentto almost 100% indium content. We have selected one In/Zn compositionfor our study. AZO tends to form rougher films due to its crystallinenature. Too much roughness can adversely affect the transmittance andconductivity of the silver layer in an IMI stack thus negating thebenefit to the Ag layer attained with appropriate AZO properties.

The absolute conductivity of the dielectric layers in the IMI stacksdoes not significantly affect the performance of the stacks since thefunctional conductivity is derived from the silver layer and thedielectric layers are too thin to function as insulators. AZO isextremely inexpensive and has the added benefit of having good adhesionto silver. In addition, silver shows enhanced properties when grown ontop of AZO due to a good crystallographic lattice match between thematerials. The chemical resistance of AZO however, is not exceptional.IZO, being chiefly comprised of indium-oxide, is expensive; however, ithas better conductivity and chemical resistance than AZO. The 15% Zn/85%In target composition was used in this example but other mixtures thathave either more or less indium can be used. In at least one embodimentit may preferred that the IZO is amorphous.

For simplicity, mechanical and chemical durability, not color ortransmittance, was the primary concern for this series of experiments,the dielectric layer thickness was fixed at 350 Å. For these initialexperiments, AZO was deposited with argon only. No oxygen was added. TheIZO layers were deposited with 4% O₂ in argon.

The coating stacks prepared and their properties are given in Table 7.In each stack, the nominal dielectric layer thickness is 350 Å and thenominal silver thickness is 110 Å. These stacks were used to produceelectrochromic mirrors. The modeled effect of having the coating next toair and electrochromic fluid are shown in Table 6. An automotive insidemirror shape was used with a highly reflective third surface coating.The IMI coated glass formed the transparent top plate. The opticalproperties of the mirror assemblies are listed in Table 7. Part “1173IEC” refers to a reference part made with ½ wave ITO as the transparentelectrode. The mirror assemblies were blow-tested to evaluate the IMIcoating adhesion. Filled mirrors were steam tested for durability.

TABLE 7 IMI coatings and their properties. % T % T Post Sheet Stack(D65-10°) Curing Oven Resistance (Ω/□) Glass|AZO|Ag|AZO 83.1 85.4 6.8Glass|AZO|Ag|IZO 80.9 83.5 7.3 Glass|IZO|Ag|AZO 85.3 86.5 6.1Glass|IZO|Ag|IZO 82.8 84.5 7.0 Full Wave ITO (2895 Å) 85.2 — 6.2 ½ WaveITO (1447 Å) 88.9 — 12.4

The transmittance data given in Table 7 corresponds to monolithic glassmeasured in air, not against EC fluid. The sheet resistances in the 6 to7 ohm range are roughly equivalent to that of full wave ITO. As shown,the transmittance of full wave ITO on 1.6 mm glass is approximately 85%.The IMI stack shows an increase in transmittance caused by thermalprocessing in the epoxy cure oven for an element whose epoxy is made andcured in accordance with the general principles described in U.S. Pat.No. 6,195,193B1 and U.S. Pat. No. 6,963,439B2. The direct comparison oftransmittance between the two transparent electrodes can only be madewhen both coatings are in contact with the EC fluid. This requireseither calculation using thin film models or measurement of an EC cellwith both materials. The modeled transmittance values for these optionsare shown in Table 8.

TABLE 8 Change in transmittance with adjacent medium (sample stackmodels). Top Ag Dielectric % T % T Sample A (A) (A) (air) (EC fluid)Change ½ λ ITO — — 88.0 92.4 +4.4 AZO|Ag|AZO 110 350 87.1 82.5 −4.6IZO|Ag|AZO|IZO 110 450 88.0 84.6 −3.4 IZO|AZO|Ag|AZO|IZO 85 500 88.287.4 −0.8 IZO|AZO|Ag|AZO|IZO 85 550 85.2 86.3 +1.1

The reflectance of the cells prepared with the IMI top plates issignificantly lower than a mirror with a ½ wave ITO top plate. Again,the sheet resistance of the IMI top plates is half that of theproduction ½ wave ITO used for the standard part. However, as statedabove, the IMI stacks from the Round-1 experiments were not optimizedfor color or transmittance. The relative reflectance for the cellslisted in Table 9 is inconsistent with the singles transmittance values.It is unclear why this is so. The transmittance change with heattreatment is consistent from sample to sample in this group. However,this change, as well as levels of adhesion and to some degree opticalconstants of materials will to some level be a function of coatingparameters and conditions. Blow test values are obtained by taking anempty element cell which has undergone curing of the epoxy and havingthe fill hole plugged, drilling a hole of approximately 1.5 mm indiameter approximately ½ inch from the edge of the element. Parts arepressurized at a rate of 0.5 or 1 psi/second and the pressure at failureis noted. The failure mechanism is also noted such as coating separatingfrom the glass or separation within the coating stack or separation ofthe epoxy within itself. Steam tests values are obtained via the testprocedure described in U.S. Pat. No. 6,195,193, entitled SEAL FORELECTROCHROMIC DEVICES, issued Feb. 27, 2001, which is hereby includedby reference.

TABLE 9 Mirror cell optical properties (GMR4 back plate, light state,averaged data). Stack % R L* a* b* Glass|AZO|Ag|AZO 70.8 87.4 −3.5 7.0Glass|AZO|Ag|IZO 69.5 86.8 −3.3 6.1 Glass|IZO|Ag|AZO 74.8 89.3 −3.8 4.0Glass|IZO|Ag|IZO 74.0 88.9 −3.8 3.4 1173 IEC Part 86.8 94.7 −3.7 6.0

Often, in order to compensate for variations in seal widths, it issometimes valuable to “normalize” the data before performing furtherstatistical analyses. One way to do this is to take the test valuemultiplied by the normal seal widths and divide this by the actual sealwidths for each individual part.

The average blow value for the AZO|Ag|AZO stack is essentiallyequivalent to the parts with ITO as the transparent electrode. For thedifferent stacks evaluated we found Glass/AZO/Ag/AZO is equivalent toITO while the other stacks were approximately 20% lower in value withsome intra-stack layer delaminations. Having an AZO layer on each sideof the silver provides the highest level of adhesion. The high blowvalue is reinforced by the total lack of lift in the IMI layer for theAZO|Ag|AZO samples. The percent of IMI coating lift is apparentlycorrelated to the layer on top of the silver; AZO again giving thebetter result. The strongest trend in the steam data is enhancedperformance for the stacks having IZO as the top layer.

In steam life testing for the same series of stacks shows on average,the IZO|Ag|IZO stack was the strongest performer in the steam testhowever the AZO|Ag|IZO stack is not far behind. Unfortunately, thestrongest performer in the blow test is the poorest performer in thesteam test. These strengths and weaknesses can be controlled to throughinnovative stack design.

The aesthetics of the element related to coloring and clearing uniformlycan be affected my many factors, including the cure profile, choice ofmaterials in the coating stack, and choice of materials in the sealmaterial.

It is presently preferred to use the materials and cure methods muchlike those described in U.S. Pat. No. 6,195,193. Because of theirexcellent adhesion to glass, low oxygen permeability and good solventresistance, epoxy-based organic resin sealing systems are preferred.These epoxy resin seals may be UV curing, such as described in U.S. Pat.No. 4,297,401, entitled LIQUID CRYSTAL DISPLAY AND PHOTOPOLYMEZIRABLESEALANT THEREFOR or thermally curing, such as with mixtures of liquidepoxy resin with liquid polyamide resin or dicyandiamide, or they can behomopolymerized. The organic sealing resin may contain fillers orthickeners to reduce flow and shrinkage such as fumed silica, silica,mica, clay, calcium carbonate, alumina, etc., and/or pigments to addcolor. Fillers pretreated with hydrophobic or silane surface treatmentsare preferred. Cured resin crosslink density can be controlled by use ofmixtures of mono-functional, di-functional and multi-functional epoxyresins and curing agents. Additives such as silanes or titanates can beused to improve the seal's hydrolytic stability and spacers such asglass beads or rods can be used to control final seal thickness andsubstrate spacing. Suitable epoxy sealing resins for use in a perimeterseal member 116 include but are not limited to: “EPON RESIN” 813, 825,826, 828, 830, 834, 862, 1001F, 1002F, 2012, DPS-155, 164, 1031, 1074,58005, 58006, 58034, 58901, 871, 872 and DPL-862 available from ShellChemical Co., Houston, Tex.; “ARALITE” GY 6010, GY 6020, CY 9579, GT7071, XU 248, EPN 1139, EPN 1138, PY 307, ECN 1235, ECN 1273, ECN 1280,MT 0163, MY 720, MY 0500, MY 0510 and PT 810 available from Ciba Geigy,Hawthome, N.Y.; “D.E.R.” 331, 317, 361, 383, 661, 662, 667, 732, 736,“D.E.N.” 431, 438, 439 and 444 available from Dow Chemical Co., Midland,Mich., meta-xylene diamine, 1,8-diamino-p-methane, isophrone diamine,1,3-bis aminomethyl cyclohexane, 1,6-hexanediamine, diethylene triamine,1,4 diamino cyclohexane, 1,3 diamino cyclohexane, 1,2 diaminocyclohexane, 1,3 pentane diamine, and 2-methylpentamethylene diamine.

Suitable epoxy curing agents include V-15, V-25 and V-40 polyamides fromShell Chemical Co.; “AJICURE” PN-23, PN-34, and VDH available fromAjinomoto Co., Tokyo, Japan; “CUREZOL” AMZ, 2MZ, 2E4MZ, C11Z, C17Z, 2PZ,2IZ and 2P4MZ available from Shikoku Fine Chemicals, Tokyo, Japan;“ERISYS” DDA or DDA accelerated with U-405, 24EMI, U-410 and U-415available from CVC Specialty Chemicals, Maple Shade, N.J.; “AMICURE”PACM, 2049, 352, CG, CG-325 and CG-1200 available from Air Products,Allentown, Pa.

Optional fillers include fumed silica such as “CAB-O-SIL” L-90, LM-130,LM-5, PTG, M-5, MS-7, MS-55, TS-720, HS-5, EH-5 available from CabotCorporation, Tuscola, Ill.; “AEROSIL” R972, R974, R805, R812, R812 S,R202, US204 and US206 available from Degussa, Akron, Ohio. Suitable clayfillers include BUCA, CATALPO, ASP NC, SATINTONE 5, SATINTONF SP-33,TRANSLINK 37, TRANSLINK 77, TRANSLINK 445, TRANSLINK 555 available fromEngelhard Corporation, Edison, N.J. Suitable silica fillers are SILCRONG-130, G-300, G-100-T and G-100 available from SCM Chemicals, Baltimore,Md. Suitable precision glass microbead spacers are optionally availablein an assortment of sizes from Duke Scientific, Palo Alto, Calif.

Optionally, silane coupling agents that may be incorporated to improvethe seal's hydrolytic stability include Z-6020 (which is the same orvery similar to A-1120 from Union Carbide), Z-6030, Z-6032, Z-6040,Z-6075 and Z-6076 available from Dow Corning Corporation, Midland, Mich.

In addition, the choice of crosslinked polymer or thickening agent,method of in situ crosslinking, choice of plug material, and theelectrochromic species used may affect whether a particular combinationof materials yields acceptable cosmetic results. Nonetheless, there is atendency for TCO materials with better bulk conductivity to be somewhatless sensitive to various cosmetic issues when placed adjacent to theelectrochromic medium.

In an experiment where the AZO oxidation level was optimized the effectsof added O₂ on the conductivity and transmittance of a glass/AZO/Agstack was shown. This will vary for different equipment and targetcompositions but the trends are indicative of some steps necessary foroptimizing this type of stack. The sheet resistance and transmittance ofthe Glass|AZO|Ag stack were optimized in this manner. The effect ofadded O₂ on the conductivity and transmittance of this stack is shown inFIG. 9. The absolute conductivity of the AZO layer itself is notimportant, only its effect on the properties of the silver layer. Thisis the rationale for the optimization route taken. The addition of 4% O₂to the argon gas feed gave optimum conductivity and transmittance. FIG.10 shows the change in the extinction coefficient (absorbtivity) androughness of the AZO with added O₂. The addition of 6% O₂ produces AZOwith lower absorbance than at 4% however the roughness is alsoincreasing. The increased roughness is the likely cause of the increasein sheet resistance observed at 6% O₂ in FIG. 9. This does suggest thepotential to slightly increase the transmission of the stack bysacrificing some conductivity.

The AZO deposited for all the stacks prepared in this series ofexperiments was sputtered with 4% O₂, as was the IZO. Table 10 lists thestacks deposited in DOE-2 for evaluation. Also included, for comparison,are the transmittance and sheet resistance of full and half-wave ITO topplates. The rationale for these stack designs is to address adhesion andsteam life. The AZO layers were placed on one or both sides of the Aglayers to improve adhesion, as measured by blow testing. The IZO wasplaced as the top most layer to help address steam lifetime. The layerthicknesses were adjusted to tune the stack for a bluish color in thedarkened state and to maximize transmittance.

The transmittance of the stack designs varies from 84.5 to 87.3 percent.The sheet resistance varies from 5.0 to 9.0 Ohm/sq. For a given Agthickness, the maximum transmittance and minimum sheet resistance occurswhen the bottom layer consists of glass/IZO/AZO/Ag. The IZO keeps thelayers smooth and the AZO enhances the microstructure of the Ag due to acrystal lattice match between the AZO and Ag. This yields improved Agconductivity and adhesion. Since the AZO layer is crystalline thesurface roughness is increased as the layer thickens. Therefore, thebi-layer of IZO/AZO provides the needed optical thickness while havingthe proper interface layer to seed the Ag. The significantly higherresistance of sample #11 is likely due to the roughness associated withthe over-thick AZO layer under the silver. This is also evident insamples 7 and 8. The roughness associated with the thick AZO base layerin sample 7 causes the observed 1 Ω/square higher sheet resistance thansample 8 which has a relatively smooth IZO base layer. The roughnesswill have more of an impact on electrical properties as the Ag layer isthinned.

The optical characterization data for the fabricated EC-elements isgiven in Table 11. An automotive inside mirror shape was used with ahighly reflective 3^(rd) surface reflector electrode where thereflectivity is essentially all coming from 7% Au 93% Ag alloy.

TABLE 10 Round-2 stack designs and properties. Stack Å R_(s) (Ω/□) % TStack Å R_(s) (Ω/sq) % T #7 #11 IZO 400 6.9 85.3 AZO 500 9.0 86.0 AZO 50Ag 80 Ag 110 AZO 480 AZO 500 Glass Glass #12 #8 IZO 500 6.5 84.5 IZO 4005.9 86.0 AZO 50 AZO 50 Ag 80 Ag 110 AZO 50 IZO 450 IZO 350 Glass Glass#9 #13 IZO 400 IZO 450 6.5 87.3 AZO 50 5.0 86.5 AZO 50 Ag 110 Ag 80 AZO50 AZO 50 IZO 400 IZO 430 Glass Glass *ITO 1447 **ITO 2895 6.2 85.2(Halfλ) 12.4 88.9 (Full λ)

TABLE 11 Average optical properties of the EC elements. Stack % R L* a*b*  7. G-AZO-Ag-AZO-IZO 75.8 89.8 −3.5 7.4  8. G-IZO-Ag-AZO-IZO 77.790.7 −4.1 4.0 13. G-IZO-AZO-Ag-AZO-IZO 79.4 91.4 −3.9 4.0 ITO IEC Part86.8 94.7 −3.7 6.0

In the second set of experiments the steam results of an AZO/Ag/AZOstack were improved by about 50% compared to the previous experiment byputting an IZO layer on as the top layer. Conversely, the steam lifeperformance was reduced by about one third with the addition of a thinAZO layer placed between the Ag and the IZO layers in an IZO/Ag/IZOstack.

The reflectance of the IMI based cells ranged from 76 to 79% incomparison to approximately 87% for an 1173 IEC part and 69 to 75% forround 1 experiments. The reflected color of the IMI based cells wasequivalent to that of production parts with #8 and #13 being slightlyless yellow than the average production part. Stack #7 producedreasonable blow numbers but showed a high failure rate at the IMI stack.Stacks 8 and 13 failed at lower blow pressures and gave very highadhesion failure rates within the IMI stack. The steam testing resultswere fairly flat and mediocre. While the best and worst stacks fromround-1 lasted between 30 and 15 days, respectively, the round-2 samplesfailed at 20 days, average. Several differences (in addition to stackdesign changes) existed between round 1 and round 2 which may haveaffected the blow and steam performance. One issue in the performance ofthe round 2 EC-cells is their lay-up. The IMI coated glass sat forseveral days prior to lay-up and showed signs of handling. Thesequencing of the layers in the coater also changed. In round 1 weproduced layers going both in the forward and backward direction in thecoater. In round 2 we produced all layers going in the forwarddirection. We also had oxygen present in the AZO layers in round 2 whichwas not present in round 1.

The cosmetic appearance of the round 2 parts matched the good appearancewe attained in round 1 with the same fluid and epoxy. Upon roomtemperature cycling at 1.2 volts the parts developed latent defectswhere fingerprints, scuff marks or other defects were present.

The performance of sample #13 was run on a final tester to generatedarkening and clearing performance for comparison to a standard product.Table 12 shows some of the performance statistics. The IMI stack #13darkened 20% faster than a standard product. The lower sheet resistanceleads to a higher current draw as expected. FIG. 13 illustrates andTable 10 lists the reflected color in the bright and dark states for theDOE2 sample numbers 7, 8 and 13.

TABLE 12 EC switching performance for stack #13 Peak 70-15 10-60 SampleMRH MRL Current Current Time Time IMI #13 82.3 8.13 142 475.7 2.56 5.12ITO 86.5 7.3 123 300.9 3.2 4.7

TABLE 13 Reflected color in the bright and dark state for DOE 2 samples7, 8 and 13 a* b* a* b* Sample Cap Y bright bright bright Cap Y darkdark dark 7 76.9 −3.5 8.5 8.8 −1.4 −3.8 8 79.7 −4.2 4.8 9.6 1 −3.6 1381.7 −4.1 4.8 8.2 −2.9 −10.4

The color of the IMI stacks in the dark state is comparable to thestandard product with ITO as the transparent electrode. The dark statereflectivity is within the design targets for flat mirrors.

The following are experimental results and wording from several sets ofexperiments loosely lumped into IMI DOE-3. Layer stress was analyzed attwo process pressures for aluminum-doped zinc-oxide (AZO), zinc-dopedindium-oxide (IZO) and metallic silver (Ag). The results indicate thatAZO has the highest compressive stress which can be decreased slightlyby processing at higher chamber pressure. Based upon the small change instress it was determined that little could be gained from processing athigher pressure. This conclusion was called into question by the resultswhich showed a potential correlation between chamber pressure andcoating lift for a particular layer design.

Order of deposition was studied to determine the sensitivity of the IMIstack to processing steps in a coater. The aim of these experiments wasto determine if there are significant risks in implementing the IMIcoating in a rotary coater which utilizes stationary substrates fordeposition. No significant change in coating properties was observed forthe differing processing methods.

Due to the sensitivity of thick AZO layers to failure in steam autoclaveexposure a series of experiments were carried out to determine theoptimum thickness of bottom and top AZO buffer layers for maximizedadhesion and steam stability. For the top buffer it was determined thatadhesion is gained with as little as 50 Å of AZO and there is noenhancement gained by thickening the AZO layer beyond that level. Forthe bottom AZO buffer layer, the results were inconclusive. As discussedabove, stress in thick AZO is significant enough to affect adhesion andlikely overwhelmed any property changes caused by the modification ofthe bottom buffer thickness.

Two sets of heat treatment tests were carried out. The first showed thatheat treatment for extended period up to 30 minutes at 300° C. do notdamage the IMI coating and actually improve its properties. A second setof experiments showed that IZO based IMI stacks perform better afterheat treatment for IZO compositions rich in zinc-oxide.

Optical modeling of IMI stacks was carried out. This modeling studiedthe effect of the dielectric index of refraction on the transmittance ofthe IMI coatings and ultimately its effect on the performance of an ECcell. The results show that the use of high index layers like TiO2 helpto give performance and color very close to what is possible with the½-wave ITO coating that is currently in use.

Layer stress in multilayered coating stacks can adversely affect theadhesion of the coating. For this reason it was important to verify thatthe dielectric layers being used in the IMI stacks under investigationwere being deposited with reasonably low stress. The argon pressureutilized for deposition was run high and low for each material todetermine the response slope for each material. The results are shown inTable 14. The stress measured for all of the coatings was reasonablylow, being less than 1 Giga-Pascal. The stress in the AZO layers washigher than the IZO layers, however the small change caused by theincreased pressure indicates that pressure tuning would have limitedbenefit. Based upon the results from these experiments, depositions forthe rest of the DOE were carried out at 3.0 mTorr.

TABLE 14 Effects of deposition pressure on layer stress: Exp. #Composition Thickness (Å) Pressure (mTorr) Stress (GPa) 1 AZO 500 3.0−0.77 2 AZO 500 5.0 −0.64 3 IZO 500 3.0 −0.20 4 IZO 500 5.0 −0.19 5 Ag500 2.0 0.04 6 Ag 500 4.0 0.05

AZO is a very good material for use in contact with a silver layer as itprovides optimum adhesion and thermal stability. Unfortunately, AZO isnot extremely stable to chemical attack. For this reason, a multilayerapproach is preferred utilizing a minimum thickness of AZO as a bufferagainst the silver layer and making up the remainder of the coatingthickness with IZO, ITO, or another dielectric which has adequate steamstability. Section 3 is broken into two parts, studying the bottom andtop AZO buffers separately. Table 15 shows the stack design and layerthicknesses utilized for this evaluation. The first half of theexperiments (13-17) investigated the effect of varying the top AZObuffer layer thickness on adhesion and steam stability. The second halfof the experiments (18-22) investigated the effect of varying the bottomAZO buffer layer thickness on adhesion. Because experiments 18 through22 used a thick AZO top layer, they were not tested for steam stabilitydue to the known weakness of a monolithic AZO top layer to this test.The averaged results of the testing are shown in Table 16. The thick AZObase layer used in experiments 13 through 17 gave very good results inboth blow and steam testing averaging 26 psi and 34 days, respectively.Being below the silver layer is adequate protection from steam autoclaveexposure. Experiments 18 through 22, which studied the thickness of theAZO bottom layer, averaged 21.5 psi in blow testing. No clear trends areapparent for the thickness of the AZO layer either above or below thesilver layer. Apparently, a 50 Å AZO buffer layer is adequate to givegood adhesion. The clearest trend from this series is the lack ofcoating lift observed for the samples with the 450 Å AZO bottom layer(exp's 13-17). Experiments 18 through 22 averaged 65% coating lift inblow testing. Also, the blow testing of the samples from experiments 13through 17 were dominated by glass breakage. The fraction of failuresdue to glass breakage for the samples from experiments 18 through 22 waslow. Instead, the failures were dominated by coating lift.Unfortunately, experiments 18-22 were probably invalidated by the factthat a thick AZO top layer was used. Apparently the strain in this thicklayer is high enough to dominate the adhesion of the IMI coating. Anyperturbation caused by the change in the thickness of the bottom AZObuffer layer was likely swamped by the stress of the top layer.

TABLE 15 AZO/IZO layer thicknesses utilized for the buffer layer study:Exp. # Glass IZO (Å) AZO (Å) Ag (Å) AZO (Å) IZO (Å) 13 450 100 50 450 14450 100 75 425 15 450 100 100 400 16 450 100 125 375 17 450 100 150 35018 400 50 100 450 19 375 75 100 450 20 350 100 100 450 21 325 125 100450 22 300 150 100 450

TABLE 16 Averaged testing results for the samples from Section 3: BlowIMI Lift Exp. # AZO Thick. (Å) (psi) (%) Steam Life (days) Top 13 5026.7 0 31.3 14 75 27.4 1 39.4 15 100 24.2 0 30.5 16 125 25.7 0 39.4 17150 25.8 0 29.5 Bottom 18 50 24.3 57 19 75 21.7 93 20 100 19.3 66 21 12520.3 64 22 150 21.9 44

The run conditions from experiment 10 were used to prepare several11.8″×16″ lites coated with the 5 layer IMI stack including IZO at 440angstroms, AZO at 50 angstroms, Ag at 80 angstroms, AZO at 50 angstroms,IZO at 449 angstroms and glass. Samples were cut from these litesmeasuring 4″×4″ in size. The optical transmittance, haze and sheetresistance of each sample was then measured as a baseline. The samples,two each, were soaked at one of the three following temperatures, 200°C., 300° C. and 400° C., for one of four times, 5 min, 10 min, 15 minand 20 min. The transmittance, haze and sheet resistance of each samplewas then re-measured and compared to its baseline values. The averageddata is presented in Table 17.

The transmittance of the IMI stacks increases for all of heat treatmentshowever the maximum change is observed for the 300° C. samples. The 400°C. samples show a reduced transmittance increase relative to the 300° C.samples. This is caused by the significant optical property change thatis also causing a significant b* shift. A potential explanation for theobserved shift of the UV absorption edge into the visible is that theIZO is being modified by the high temperature. A second possibleexplanation is that the Ag surface plasmon band is shifting at hightemperature due to a chemical or structural change at the AZO/Aginterfaces. This is less likely based on the observed high temperatureresponse of existing Ag/AZO based low emissivity coatings.

TABLE 17 Average IMI property changes with heat treatment: InitialChange Temp (° C.) Soak Time (min) % T % H R_(sheet) b* Δ % T Δ % Haze ΔR_(sheet) Δ b* 200 5 85.54 0.011 7.3 7.8 0.21 −0.001 −0.2 −0.1 200 1085.37 0.007 7.0 8.2 0.71 0.001 −0.5 −0.5 200 15 85.23 0.013 7.0 8.1 0.87−0.007 −0.5 −0.4 200 20 85.39 0.007 7.4 8.0 0.94 0.002 −0.4 −0.3 300 584.98 0.009 6.9 9.0 1.23 0.001 −0.7 −0.5 300 10 85.45 0.007 7.3 8.1 1.680.001 −0.9 0.4 300 15 85.50 0.008 7.0 7.8 1.64 0.011 −1.0 0.3 300 2085.06 0.007 6.9 8.8 1.60 0.002 −1.0 0.7 400 5 85.58 0.006 7.0 7.5 1.660.002 −0.9 1.1 400 10 84.99 0.007 7.0 8.9 1.02 0.016 −0.6 5.3 400 1585.41 0.006 7.4 7.9 1.24 0.014 −0.4 7.5 400 20 85.53 0.006 7.1 7.5 1.610.018 −0.1 7.6

For the purposes of these experiments, haze is defined as thenon-specular component of the surface reflectance (Y_(R)). At both 200°C. and 300° C. there was no measurable change in haze. This was alsotrue for the shortest soak duration (5 min) at 400° C. The longer soakdurations at 400° C. produced a measurable increase in haze; however thetotal haze was still minimal.

As was the case for transmittance, all of the heat treatments decreasedthe sheet resistance. The 300° C. treatments caused more improvementthan the 200° C. experiments. The 400° C. experiments gave good resultsat 5 minutes, which were comparable to the 300° C. results. Beyond 5minutes at 400° C., the improvement in sheet resistance was graduallylost, leaving the 20 minute samples almost equivalent to their pre-heatconductivity. If all of the IMI stacks were heat treated at 300° C. forbetween 10 and 15 minutes to achieve optimum characteristics.

These results indicate that any heat treatment or epoxy cure methodlikely to be employed in production will improve the IMI performancerather than degrade it. Increasing the temperature of the epoxy cureoven to 300° C. would be best for optimizing the properties of the IMIcoating, however, it would likely not be advantageous for the epoxyperformance.

The following relates to samples of three layered IMI stacks forevaluation. These stacks benefit from the combinatorial sputteringcapabilities at the National Renewable Energy Laboratory (NREL) in thatthe dielectric layers of each sample form a compositional gradientacross the sample, allowing multiple compositions of IZO to besimultaneously evaluated. IZO is a non-specific combination ofindium-oxide (In₂O₃) and zinc-oxide (ZnO). Commonly, ˜20% Zn is used foroptimum conductivity however we would like to preferentially optimizethe physical and chemical properties of the IZO to improve the stabilityand adhesion of the IMI stack. The absolute conductivity of thedielectric layers is not very important to the performance of the IMIstack. Four libraries of indium-zinc compositions were applied onto2″×2″ glass substrates (1.1 mm) as three layer IMI stacks: basedielectric (400 Å), silver (100 Å), top dielectric (400 Å). In eachcase, as close to a uniform dielectric and silver thickness as possiblewas deposited. Because the NREL system uses small, 2″ toroidalmagnetrons and a stationary substrate, the uniformity is less thanoptimal. For this and several other reasons we have set up acombinatorial system in the Temescal coater with 3″ toroidal magnetronsand linear motion that will give better uniformity and repeatabilitythan the system at NREL. The composition ranges of the four librariesare listed in Table 18.

TABLE 18 Composition ranges of the four libraries: Library IndiumFraction (atomic %) L1  4-15% L2 15-50% L3 35-70% L4 70-95%

Prior to heat treatment, the baseline values of transmittance, sheetresistance and haze was measured in 5 positions across each sample. Thesamples were then put through an epoxy cure oven (line 502) set forstandard production (200° C.). The transmittance, sheet resistance andhaze were then remeasured. The results are presented in Table 19. Thedata can be broken down by the In/Zn ratio. The low In, high Zn, contentdielectrics produced IMI stacks with higher transmittance and lowersheet resistance. The haze was comparable before heat treatment. Afterheat treatment there was an increase in haze at very high Zn content,but a much larger increase for the In rich samples. The large hazeincrease is a possible indication of crystallization of the IZO duringthe heat treatment. This behavior has been documented in the literaturefor compositional extremes of IZO.

TABLE 19 IMI properties before and after heat treatment: LibraryBaseline Post-Heat Change ~% In % T % Haze R_(Sheet) % T % HazeR_(Sheet) Δ% T Δ% H ΔR_(Sheet) L1 1 4 85.11 0.049 8.6 84.77 0.066 8.5−0.34 0.017 −0.1 2 6.5 87.48 0.037 7.6 87.21 0.06 7.2 −0.27 0.023 −0.4 39 86.48 0.036 8.2 86.31 0.054 7.7 −0.17 0.018 −0.5 4 11.5 86.26 0.0369.1 85.86 0.05 8.7 −0.4 0.014 −0.4 5 14 83.99 0.039 12.5 83.51 0.08410.6 −0.48 0.045 −1.9 L2 1 16 85.76 0.044 11.8 86.1 0.046 10 0.34 0.002−1.8 2 24.5 87.52 0.034 8.8 88.05 0.032 8.2 0.53 −0.002 −0.6 3 33 87.50.036 9.3 88.03 0.038 8.4 0.53 0.002 −0.9 4 41.5 87.08 0.023 10.7 87.370.03 10.6 0.29 0.007 −0.1 5 50 86.17 0.011 14.4 86.21 0.017 13.2 0.040.006 −1.2 L3 1 35 85.58 0.04 11.4 86.29 0.04 9.8 0.71 0 −1.6 2 43.586.34 0.036 9 87.16 0.049 8.5 0.82 0.013 −0.5 3 52 86.33 0.038 9.3 87.230.048 8.8 0.9 0.01 −0.5 4 60.5 86.07 0.04 10.3 87.12 0.053 9.7 1.050.013 −0.6 5 69 85.77 0.049 12.7 86.97 0.051 11.5 1.2 0.002 −1.2 L4 1 7183.67 0.011 17.3 83.72 0.022 15.6 0.05 0.011 −1.7 2 77 85.88 0.013 13.585.88 0.041 13.1 0 0.028 −0.4 3 83 86.12 0.023 12.9 86.15 0.1 12 0.030.077 −0.9 4 89 85.53 0.032 13.5 85.72 0.175 12.3 0.19 0.143 −1.2 5 9579.98 0.031 17 80.6 0.126 16 0.62 0.095 −1

The results of these experiments are very interesting. IZO, in general,is deposited at approximately 20% ZnO content to maximize conductivity.The conductivity of the IMI stack is not very sensitive to the absoluteconductivity of the dielectric layers used on either side of the silver.The high ZnO content range (˜70%) of the combinatorial samples showedthe best performance in heat treatment. Even though the conductivity ofthe IZO layers is poor at high zinc content, the overall conductivity ofthe IMI stack was highest in this range. Post heat treatment haze andtransmittance was also optimum at high ZnO content. If ˜30% In₂O₃content is high enough to give adequate steam performance whilemaintaining adequate adhesion then a 3 layer design may be feasible forthe IMI stack.

Optical modeling was conducted as part of an evaluation of the benefitsof alternative dielectric layers and to support some patentdocumentation. The aim of the modeling was to quantify the potentialimprovements to the color and transmittance of the IMI stacks throughmaterial substitutions. As was described in the second IMI DOE report,the transmittance of coated glass can change considerably depending onwhether the exit medium is air or propylene-carbonate (PC) solution. Inthe case of ½-wave ITO on glass, the modeled transmittance improves from88.0% against air to 92.4% against propylene-carbonate. For simplicity,3 layer stacks were used in the model, (Table 20). The addition of 50 ÅAZO buffer layers above and below the Ag layer have minimal effect onthe optical properties of the stack.

TABLE 20 Stack design used for Section 5. Exit MediumPropylene-Carbonate Dielectric 250 to 600 Å Ag  25 to 200 Å Dielectric250 to 600 Å Glass Entrance Medium Air

Four dielectric materials were chosen for evaluation covering a range ofrefractive index from medium to high. These materials are TiSi₂O₆ (1.7),IZO (2.0), cold TiO₂ (2.4) and hot TiO₂ (2.8). In the original study,the stacks were optimized for both air and propylene-carbonate exitmediums. The data presented here is based entirely upon optimization forthe propylene-carbonate case. For each dielectric material, several Agthicknesses were evaluated. The data is presented in Table 21. In eachexample, a dielectric material and a silver thickness were chosen. Then,utilizing TFCalc, the dielectric layer thicknesses were refined to giveoptimum transmittance. For comparison, in each case the transmittancefor the air exit medium is also given. For the two low index cases, thetransmittance in air is higher for the thin Ag cases. The relationshipreverses for the thicker Ag cases which have higher transmittanceagainst propylene-carbonate. Both of the TiO₂ cases uniformly gavehigher transmittance against propylene-carbonate. For silver thicknessabove about 30 Å, optimum transmittance is obtained through the use ofhigh index dielectric layers like TiO₂. To obtain a 6 Ω/square IMIcoating requires a Ag layer approximately 100 Å in thickness. Color wascalculated for the 100 Å Ag layer cases with Cr/Ru back reflectors. Thisdata is presented in Table 22. An identically calculated OEC cell(½-wave ITO) is included for comparison. The high light statereflectance of the TiSi₂O₆ case is misleading. A significant fraction ofthe reflectance is coming from the second surface, as is indicated bythe very high dark state reflectance. The reflected color is somewhatgreen in the light state and very bronze in the dark state. For the IZOcase, light state reflectance was lower and somewhat green. The IZO celldark state reflectance is only slightly higher than the reference OECcell and very neutral. The light state reflectance of the TiO₂ cell isonly 1 percent lower than the reference and the hue is the same as theIZO cell, slightly green. The dark state has very low reflectance and anessentially neutral color. The hot TiO₂ cell gives reflectance higherthan the reference cell and a very neutral color. The dark state has lowreflectance and a slightly purple hue.

TABLE 21 Optical data from IMI stack modeling (thickness in Å): TiSi₂O₆Ag TiSi₂O₆ % T % T-Air IZO Ag IZO % T % T-Air 557 25 504 94 91.7 514 25493 90.6 85.3 479 50 472 91 92.7 429 50 418 91 87.5 491 75 488 85 90.5384 75 388 89.4 89.2 506 100 504 77 85.4 397 100 401 85.2 88.4 519 125517 68 78.1 407 125 410 79 85   530 150 529 58.9 69.7 415 150 418 71.679.6 TiO₂ Ag TiO₂ % T % T-Air TiO₂ (hot) Ag TiO₂ (hot) % T % T-Air 48450 440 92.9 89.1 451 50 409 92 87.7 434 75 410 92.86 89.3 410 75 38692.2 88.1 383 100 371 92.6 89.7 371 100 356 92.3 88.6 340 125 336 91.690.5 330 125 323 92.1 89.3 326 150 324 88.8 90.64 302 150 298 90.8 90.2323 175 322 84.2 88.8 292 175 290 87.8 89.9 323 200 322 78 85 288 200288 82.9 87.7

TABLE 22 Cell color for the transmittance optimized stacks (100 Å Agcase):

*Full cell with ½-wave ITO top plate and identical back plate and fluid.

A three layered IMI stack (100 A Ag) based on AZO, IZO, ITO or somecombination of these materials will be limited to about 52.8%reflectance for an OEC type Ru based mirror. A similarly modeledstandard ½ wave ITO based cell will have about 60.1% reflectance. Inorder to increase the reflectance of an IMI based cell to the levelcurrently obtained for ½ wave ITO we will need to incorporate high indexlayers such as the TiO₂ used in the models. A five layer IMI stackincorporating TiO₂ will likely approach 59.2% reflectance. A higherindex material will allow cell reflectance to approach 60.3% which isactually slightly higher than the standard cell. A single TiO₂ layerdeposited onto the glass, below the IMI stack will give a reflectance ofapproximately 57.8% If it is necessary that the transmittance of the IMIcoating be as high as ½ wave ITO then high index layers will have to bepart of the stack.

The present inventive electrochromic element includes a transparentelectrode whose components reduce the overall cost of the electrochromicelement without sacrificing optical and physical characteristics, suchas reflectivity, color, electrical switch stability, environmentaldurability and the like. Moreover, the inventive electrochromic elementis relatively easy to manufacture, assists in providing a robustmanufacturing process, provides versatility in selection of componentsutilized in constructing insulator/metal/insulator stacks, and allowstailored construction thereof to achieve particular optical and physicalproperties.

The above description is considered that of the preferred embodimentsonly. Modifications of the invention will occur to those skilled in theart and to those who make or use the invention. Therefore, it isunderstood that the embodiments shown in the drawings and describedabove are merely for illustrative purposes and are intended to beincluded within, but not intended to limit the scope of the invention,which is defined by the following claims as interpreted according to theprinciples of patent law, including the doctrine of equivalents.

1. An electrochromic element comprising: a first substrate having afirst surface and a second surface opposite the first surface; a secondsubstrate having third and fourth surfaces, the first and secondsubstrates disposed in a parallel and spaced apart relationship so as todefine a gap therebetween, the second and third surfaces opposing eachother; an electrochromic medium located in the gap, the electrochromicmedium having a light transmittance that is variable upon theapplication of an electric field thereto; and a transparent electrodelayer covering at least a portion of at least a select one of the secondsurface and the third surface, wherein the transparent electrode layercomprises a stack including a first insulator layer, at least one metallayer and a second insulator layer, and wherein the transparentelectrode layer is characterized by a color rendering index of greaterthan or equal to
 80. 2. The electrochromic element of claim 1, whereinthe transparent electrode layer is characterized by a color renderingindex of greater than or equal to
 90. 3. The electrochromic element ofclaim 2, wherein the transparent electrode layer is characterized by acolor rendering index of greater than or equal to
 95. 4. Theelectrochromic element of claim 1, wherein the at least one metal layeris a single metal layer comprises silver, and wherein the single metallayer has a thickness of between 50 angstroms and 500 angstroms.
 5. Theelectrochromic element of claim 4, wherein the single metal layer has athickness of between 75 angstroms and 250 angstroms.
 6. Theelectrochromic element of claim 5, wherein the single metal layer has athickness of between 100 angstroms and 150 angstroms.
 7. Theelectrochromic element of claim 1, wherein a total thickness of thestack including the first insulator layer, the at least one metal layerand the second insulator layer is between 100 angstroms and 700angstroms.
 8. The electrochromic element of claim 1, wherein a solarheat gain coefficient of the electrochromic element in the clear stateis less than or equal to 0.70.
 9. The electrochromic element of claim 8,wherein the solar heat gain coefficient of the electrochromic element isless than or equal to 0.50.
 10. The electrochromic element of claim 9,wherein the solar heat gain coefficient of the electrochromic element isless than or equal to 0.30.
 11. An electrochromic element comprising: afirst substrate having a first surface and a second surface opposite thefirst surface; a second substrate having third and fourth surfaces, thefirst and second substrates disposed in a parallel and spaced apartrelationship so as to define a gap therebetween, the second and thirdsurfaces opposing each other; an electrochromic medium located in thegap, the electrochromic medium having a light transmittance that isvariable upon the application of an electric field thereto; and atransparent electrode layer covering at least a portion of at least aselect one of the second surface and the third surface, wherein thetransparent electrode layer comprises a stack including a firstinsulator layer, at least one metal layer and a second insulator layer,wherein at least one of the first insulator layer and the secondinsulator layer comprises at least a select one of indium zinc oxide,indium tin oxide, aluminum zinc oxide, titanium oxide, zinc oxide,electrically conductive TiO2, CeOx, tin dioxide, silicon nitride,silicon dioxide, ZnS, chromium oxide, niobium oxide, ZrOx, WO₃, nickeloxide, IrO₂ and wherein the insulating layer of the stack that is incontact with the electrochromic medium has a resistance of greater thanor equal to 10 MOhms.
 12. An electrochromic element comprising: a firstsubstrate having a first surface and a second surface opposite the firstsurface; a second substrate having third and fourth surfaces, the firstand second substrates disposed in a parallel and spaced apartrelationship so as to define a gap therebetween, the second and thirdsurfaces opposing each other; an electrochromic medium located in thegap, the electrochromic medium having a light transmittance that isvariable upon the application of an electric field thereto; atransparent electrode layer covering at least a portion of at least aselect one of the second surface and the third surface, wherein thetransparent electrode layer comprises a stack including a firstinsulator layer, at least one metal layer and a second insulator layer;and a barrier layer positioned between the first insulator layer of thestack and the select surface that the transparent electrode layercovers, wherein at least one of the first insulator layer and the secondinsulator layer comprises at least a select one of indium zinc oxide,indium tin oxide, aluminum zinc oxide, titanium oxide, zinc oxide,electrically conductive TiO2, CeOx, tin dioxide, silicon nitride,silicon dioxide, ZnS, chromium oxide, niobium oxide, ZrOx, WO₃, nickeloxide, IrO₂, and wherein the barrier layer comprises at least a selectone of ruthenium, NiCr, NiCrOx, copper, titanium, niobium, nickel,palladium, platinum, and combinations thereof
 13. The electrochromicelement of claim 12, wherein the barrier layer has a thickness of lessthan or equal to 40 angstroms.
 14. The electrochromic element of claim13, wherein the thickness of the barrier layer is less than or equal to20 angstroms.
 15. An electrochromic element comprising: a firstsubstrate having a first surface and a second surface opposite the firstsurface; a second substrate having third and fourth surfaces, the firstand second substrates disposed in a parallel and spaced apartrelationship so as to define a gap therebetween, the second and thirdsurfaces opposing each other; an electrochromic medium located in thegap, the electrochromic medium having a light transmittance that isvariable upon the application of an electric field thereto; atransparent electrode layer covering at least a portion of at least aselect one of the second surface and the third surface, wherein thetransparent electrode layer comprises a stack including a firstinsulator layer, at least one metal layer and a second insulator layer;and a barrier layer positioned between the first insulator layer of thestack and the select surface that the transparent electrode layercovers, wherein at least one of the first insulator layer and the secondinsulator layer comprises at least a select one of indium zinc oxide,indium tin oxide, aluminum zinc oxide, titanium oxide, zinc oxide,electrically conductive TiO2, CeOx, tin dioxide, silicon nitride,silicon dioxide, ZnS, chromium oxide, niobium oxide, ZrOx, WO₃ nickeloxide, IrO₂, and wherein the barrier layer comprises at least a selectone of silica, doped silica, phosphorus-doped silica, amorphous alumina,aluminum phosphate, SiN, and SnZnOx.
 16. The electrochromic element ofclaim 15, wherein the barrier layer has a thickness of less than orequal to 150 angstroms.
 17. The electrochromic element of claim 16,wherein the thickness of the barrier layer is less than or equal to 100angstroms.
 18. The electrochromic element of claim 17, wherein thethickness of the barrier layer is less than or equal to 50 angstroms.19. An electrochromic element comprising: a first substrate having afirst surface and a second surface opposite the first surface; a secondsubstrate having third and fourth surfaces, the first and secondsubstrates disposed in a parallel and spaced apart relationship so as todefine a gap therebetween, the second and third surfaces opposing eachother; an electrochromic medium located in the gap, the electrochromicmedium having a light transmittance that is variable upon theapplication of an electric field thereto; and a transparent electrodelayer covering at least a portion of at least a select one of the secondsurface and the third surface, wherein the transparent electrode layercomprises a stack including a first insulator layer proximate theelectrochromic medium, at least one metal layer and a second insulatorlayer, and wherein the first insulator comprises indium tin oxide, andwherein the transmittance of the transparent electrode is greater thanor equal to about 75%.
 20. The electrochromic element of claim 19,wherein in the first insulating layer that is in contact with theelectrochromic medium has a resistance of greater than or equal to 10MOhms.
 21. The electrochromic element of claim 19, further comprising: abarrier layer positioned between the first insulator layer of the stackand the select surface that the transparent electrode layer covers,wherein the barrier layer comprises at least a select one of ruthenium,NiCr, NiCrOx, copper, titanium, niobium, nickel, palladium, platinum,and combinations thereof.
 22. The electrochromic element of claim 21,wherein the barrier layer has a thickness of less than or equal to 40angstroms.
 23. The electrochromic element of claim 22, wherein thethickness of the barrier layer is less than or equal to 20 angstroms.24. The electrochromic element of claim 19, further comprising: abarrier layer positioned between the first insulator layer of the stackand the select surface that the transparent electrode layer covers,wherein the barrier layer comprises at least a select one of silica,doped silica, phosphorus-doped silica, amorphous alumina, aluminumphosphate, SiN SnZnOx or other chemically inert, non-absorbingdielectric layers and combinations thereof.
 25. The electrochromicelement of claim 24, wherein the barrier layer has a thickness of lessthan or equal to 150 angstroms.
 26. The electrochromic element of claim25, wherein the thickness of the barrier layer is less than or equal to100 angstroms.
 27. The electrochromic element of claim 26, wherein thethickness of the barrier layer is less than or equal to 50 angstroms.28. An electrochromic element comprising: a first substrate having afirst surface and a second surface opposite the first surface; a secondsubstrate having third and fourth surfaces, the first and secondsubstrates disposed in a parallel and spaced apart relationship so as todefine a gap therebetween, the second and third surfaces opposing eachother; an electrochromic medium located in the gap, the electrochromicmedium having a light transmittance that is variable upon theapplication of an electric field thereto; and a transparent electrodelayer covering at least a portion of at least a select one of the secondsurface and the third surface, wherein the transparent electrode layercomprises a stack including a first insulator layer, a metal layer, anda second insulator layer, and an electrical stabilization layerpositioned between the metal layer and at least one of the insulatorlayers, wherein the electrical stabilization layer increases a value ofa breakdown potential of the metal layer by at least about 0.05 volts.29. The electrochromic element of claim 28, wherein the metal layercomprises silver.
 30. The electrochromic element of claim 28, whereinthe electrical stabilization layer comprises at least one of gold,ruthenium, rhodium, palladium, cadmium, copper, nickel, platinum, andindium.
 31. The electrochromic element of claim 28, wherein theelectrical stabilization layer increases the value of a breakdownpotential of the metal layer by about 0.10 volts.
 32. The electrochromicelement of claim 28, wherein the electrical stabilization layerincreases the value of a breakdown potential of the metal layer by about0.20 volts.
 33. The electrochromic element of claim 28, wherein theelectrical stabilization layer increases the value of a breakdownpotential of the metal layer by about 0.30 volts.
 34. The electrochromicelement of claim 28, wherein the metal layer is alloyed with a noblemetal that is different than a base metal of which the metal layer iscomprised.
 35. The electrochromic element of claim 28, wherein the metallayer is doped with at least a select one of indium and titanium. 36.The electrochromic element of claim 35, further including: a barrierlayer located between the select surface and the first insulator layerof the stack, wherein the barrier layer comprises at least a select oneof silica, doped silica, phosphorus-doped silica, amorphous alumina,aluminum phosphate, SiN SnZnOx or other chemically inert, non-absorbingdielectric layers and combinations thereof.
 37. The electrochromicelement of claim 36, wherein the barrier layer is amorphous.
 38. Theelectrochromic element of claim 28, wherein the metal layer is dopedwith at least a select one of palladium, copper, indium, titanium, andcombinations thereof.
 39. An electrochromic element comprising: a firstsubstrate having a first surface and a second surface opposite the firstsurface; a second substrate having third and fourth surfaces, the firstand second substrates disposed in a parallel and spaced apartrelationship so as to define a gap therebetween, the second and thirdsurfaces opposing each other; an electrochromic medium located in thegap, the electrochromic medium having a light transmittance that isvariable upon the application of an electric field thereto; and atransparent electrode layer covering at least a portion of at least aselect one of the second surface and the third surface, wherein thetransparent electrode layer comprises a stack including a firstinsulator layer, a metal layer, and a second insulator layer, whereinthe metal layer comprises silver and at least one of the first insulatorlayer and the second insulator layer comprises at least one of zincoxide and Sb, and wherein any of the first and second insulator layershas an absolute stress of less than 3 GPa.
 40. The electrochromicelement of claim 39, wherein the absolute stress of any of the first andsecond insulator layers is less than 1.5 GPa.
 41. The electrochromicelement of claim 40, wherein the absolute stress of any of the first andsecond insulator layers is less than 0.5 GPa.